 money and get many more features.  
I am noticing that all of the features of these systems require add on licences.  I have heard of Asterisk, and see that it's implemented in both Zentyal and Clearos.  I am a capable Linux admin, but I know next to nothing about voip.  
So, I am looking for sound advice from people who know their stuff and/or have been in the same place and found/installed a FOSS solution that worked.  What hardware recommendations are there?  What is the best way to handle QOS?  Do we need seperate network runs to each phone and computer, or can there be one network run to each station with a l2 switch and have QOS handled at the backbone switch? 
My current network: 
-We will be getting a new EOC (ethernet over copper) line installed with 5 mpbs up/down within a month.
-We have all unmanaged netgear switches, and will be separately upgrading to a pfsense based firewall to connect WAN to LAN.  We will be upgrading to whatever managed switch for the backbone is decided to be adequate.
-There are about 30 user computers total, with 5 servers.  Three servers running debian linux and two running Windows server 2003.  

A:

ServerFault doesn't really do shopping advice - you need to consult with vendors and decide what system works best for you.
Some points to consider:

Do you want a fully VOIP system (IP within the office, your PBX connects via VOIP to a provider that connects you to the PSTN), or a hybrid system (IP within the office, and your PBX connects to the PSTN directly)?
Do you want integration with Outlook/Exchange?
Do you want a vendor-supported solution, or are you comfortable with a more DIY approach?
What features do you want on your phones (voice, video, multiple lines, color screens, etc.)
How much are you willing to spend?

Some of the other points you bring up:
QOS
Depending on your network you will need to implement some kind of QoS (internally and/or externally) to ensure that VOIP traffic isn't delayed (latency/jitter is a KILLER).
Infrastructure
Many (if not most) VOIP phones have a built-in pass-through switch and support VLAN tagging, so
money and get many more features.  
 I am noticing that all of the features of these system command add on licences.   I have heard of Asterisk, and witness that it's implemented in both Zentyal and Clearos.   I am a capable Linux admin, but I sleep together next to nothing about voip.  
 indeed, I am looking for healthy advice from people who know their material and/or have been in the same place and found / installed a FOSS solution that exploit.   What hardware recommendations are there?   What is the best way to handle QOS?   Do we need seperate net runs to each phone and computer, or can there be one net run to each station with a l2 switch and have QOS handled at the backbone substitution? 
 My current network: 
 -We will be receive a new EOC (ethernet over copper) line install with 5 mpbs up / down within a month. 
 -We have all unmanaged netgear switches, and will be separately upgrading to a pfsense free-base firewall to connect WAN to LAN.   We will be upgrading to whatever managed switch for the backbone is decided to be adequate. 
 -There are about 30 user computers total, with 5 waiter.   Three servers running debian linux and two run Windows waiter 2003.  

 A: 

 ServerFault doesn't very do shopping advice - you need to confer with vendors and decide what arrangement works best for you. 
 Some point to consider: 

 Do you want a fully VOIP system (IP within the office, your PBX connects via VOIP to a supplier that connects you to the PSTN), or a hybrid system (IP within the office, and your PBX connects to the PSTN directly)? 
 Do you want integration with Outlook / Exchange? 
 Do you desire a seller - corroborate solution, or are you comfortable with a more DIY approach? 
 What features do you want on your earphone (voice, video, multiple lines, semblance screens, etc .) 
 How much are you willing to spend? 

 Some of the other points you lend up: 
 QOS 
 Depending on your network you will necessitate to implement some kind of QoS (internally and/or outwardly) to ensure that VOIP traffic isn't delayed (latency / jitter is a killer whale). 
 Infrastructure 
 Many (if not most) VOIP phones have a built - in pass - through switch and digest VLAN tagging, so
 mojey and get many more fextures.  
I am nojixing tiat all of the weatures of these systems reeuure aed on licences.  I have heard of Asterisj, anv see that it's implementcb in glth Veityal and Clearps.  I am a capable Linux aamnn, but I know next to nothing about doip.  
Sp, L am looking fjr sptnd zdvice from people who know their atuff aid/or have been on the same place and founf/inshalled a FOSS soluhion that wirkeq.  What hardwxre recommtnbations are there?  What is the best way to handke QOS?  Do ww nfgd seperate ietworh runs to eagn phona and cpmputer, or can thxre ve one network run to each station with a l2 switwh and have QOS hanelwd at the bacyvond ssivch? 
My cugreit network: 
-Se will be tetting a new EOC (euhewbet over coppsr) linq ynstalled with 5 mpbs up/down within a motth.
-Se have all unmanaged nwtgear switches, and wlll be se[arately upgrading to a pfsense based firewall to connxcg WCK gi PAN.  We will be upgrading to whatever managed awotbh for the backboke is decided to br wdrzuate.
-There arg about 30 uaer computers totap, with 5 servwrs.  Thret serfers running debian linux abd two runniug Qindows server 2003.  

A:

DerverFault doexn't rrally do shopping advicz - you need to cojsult witg vendors and deckde wvat systto works best for rou.
Some piintx to covsidgr:

Do yot want a fklly YMIP system (IP withln thg offiwe, your PBD connects via VOIP to a providxc that connecjs fou to the 'STN), ov a hybrid systqm (IP within tke officz, and hour PBX cknnects to the PSTG directly)?
Do flu want intejration wyth Iutliok/Exchxvge?
Do you want a vendor-supported wolution, or are yom comwkrtable with a nort EIY approach?
Whst weaeuges dj you want on youf pfpnes (xoice, video, oultople lines, color scraens, etc.)
How much are ypu willing to spenq?

Some of the pther points you bging np:
QOS
Dxpendimg jn your network you will need fo implemfnt some kind os QoW (internally and/or externally) to ensure that VOIP tcaffic isn't delayed (lajency/jitter is a KILLGR).
Ikfrastructurx
Many (yf not movt) VOIP phones have q built-in pass-thrpugh switch and suppodt VLAT taghing, so
money and get many more features. I that of the of these systems have of Asterisk, and that it's implemented both Zentyal and Clearos. I am capable Linux admin, but I know next to nothing about voip. So, I looking for sound advice from people who know their stuff and/or have been the place found/installed FOSS solution that worked. What hardware recommendations are there? What is the best way to handle Do we need seperate network runs to each and computer, or can be one network run to station a l2 and QOS at the backbone My current network: -We will be getting a new EOC (ethernet over copper) line installed with 5 up/down within -We have unmanaged switches, will be separately a pfsense based firewall to connect We will be upgrading to whatever managed switch the backbone decided to be adequate. -There are 30 user computers total, with 5 servers. Three running debian linux and two running Windows server 2003. A: ServerFault doesn't really do shopping you need to consult vendors and decide system best you. points to Do you want a fully VOIP system (IP within the office, PBX connects via VOIP to a provider that connects you PSTN), a hybrid system within the office, and PBX to the PSTN directly)? want with want vendor-supported or are you comfortable a more DIY approach? What do you want on lines, color screens, etc.) How much are you to spend? Some of the other points bring up: QOS Depending on your network you will need to implement kind of and/or externally) to ensure that VOIP traffic isn't (latency/jitter is a KILLER). Many (if not most) VOIP phones have a built-in switch support VLAN so
 money and get many more featurEs.  
I am noticIng thAt aLl oF tHe feAturEs of these systeMS reqUire add on licences.  I have Heard Of aSterISk, And seE that it'S ImPLEmeNtEd In bOtH zeNtyal And clearos.  i am a capablE LiNuX admin, but I knOW nExt to nothiNg aBout voip.  
So, I aM loOking fOr SouND adviCe fRom peOple whO Know thEir stuff aNd/OR have bEEn in the SAMe PlacE and found/installeD A FosS solution that Worked.  whAT hARDwaRe rEcommendatIoNs are THere?  WhaT Is THE BesT Way to handle QOs?  Do we need sePEraTe netwOrK ruNS to eacH phonE aND coMputer, or can TherE be one netWork ruN To each sTAtion wiTh a l2 swItcH anD havE qOs hAndLeD At tHE bAckBOne Switch? 
My CuRrEnt neTworK: 
-wE WIll bE geTtinG a new eOC (ethernet ovEr cOppeR) LinE instAlled With 5 MpBs up/dOwn witHin a mOnTh.
-We have all unmaNageD netgear sWitChEs, aNd Will bE SeparaTelY upGrading To a pfseNSe bAsED FIrEwall to connect WAN tO Lan.  we Will be upGradinG To WhATever manAgEd sWitcH FOr the BackBOnE is decidEd to be ADeQuAte.
-TherE aRe abouT 30 uSer ComPuterS TotaL, with 5 sErvers.  ThRee seRVers running debIAn linux and two RUnNINg wIndoWs sErver 2003.  

A:

ServeRFauLT doeSn't rEAlLy dO ShoppIng adViCE - yOU need to consult with vEnDors anD deciDe what system wOrks best foR YOU.
Some poiNts tO CoNSider:

Do you want A fullY VOIP systeM (iP within The ofFice, your pBX connecTS Via VOIP tO a pRovIdeR thAT CoNnects you to thE psTN), oR a Hybrid sYstEm (IP witHin The OffIce, AnD your PBX cOnnects tO tHe pStN DirEctly)?
dO you want InTegRaTioN with oUtlook/exchaNge?
DO yOu WAnt A vendor-SUpPORted SoLuTion, Or aRe You coMforTAblE with a mOre DIY appRoaCH?
WhaT fEaTures do You want on your PhOnes (voice, vIdEo, mUltiplE LInes, coloR screens, etc.)
How much are yoU Willing To sPend?

SOme oF the other PoiNts you BriNG up:
QOS
dependIng on YoUr nETWork yOU WiLl nEeD to implemeNT SomE kind Of qoS (iNternalLy and/or externally) tO EnsUre that VOIP trAffIc isN'T DeLayED (lATenCy/JIttER Is a KILLER).
InfrasTructure
MaNy (IF nOt most) VOIP PHonEs Have a buIlt-in paSs-thrOUgh switCh and suppOrt VLAN taGgIng, sO
 money and get many more f eatures. 
I am  no tic in g th at a ll of the feat u resof these systems requi re ad do n li c en ces. I have he a r d o fAs ter is k ,and s eethat it 's impleme nte din both Zent y al  and Clear os.   I am a cap abl e Linu xadm i n, bu t I  know  nextt o noth ing about  v o ip.  S o, I am l oo king  for sound advice fr o m people who k now th ei r  s t u ffand /or have b ee n int he same pl a c e  an d  found/instal led a FOSSs olu tion t ha t w o rked. What  h a rdw are recomme ndat ions arethere?  What i s  the be st way  to  ha ndle QO S?   D ow e n e ed  se p era te netwo rk  r uns t o ea c h p hone  an d co mpute r, or can the rebe o n e n etwor k run  toea ch st ationwithal2 switch and h aveQOS handl edat  th ebackb o ne swi tch ? My curr ent net w ork :- W ewill be getting ane w EO C (ether net ov e rco p per) lin eins tall e d  with  5 m p bs  up/down  withi n  a  m onth.
- We  haveal l u nma naged netg ear sw itches,and w i ll be separate l y upgrading t o  a p fs e nsebas ed firewall  toc onne ct W A NtoL AN. We wi ll be upgrading to whatev er  manag ed sw itch for thebackbone i s d ecided t o be ad e quate.
-Thereare a bout 30 us e r comput ers t otal, wi th 5 serv e r s.  Thre e s erv ers  ru n n in g debian linu x andtw o runni ngWindows  se rve r 2 003 . 

A:

Se rverFaul tdo es n' t r eally do shopp in g a dv ice  - yo u  needto co nsul twi t h v endorsa nd d ecid ewh at s yst em  work s be s t f or you. 
Some poi nts to c on si der:

D o you want afu lly VOIP s ys tem  (IP w i t hin theoffice, your PBX connec t s via V OIP  to a  pro vider tha t c onnect s y o u to t he PST N), o ra h y b rid s y s te m ( IP  within th e off ice,an d yo ur PBXconnects to the PS T N d irectly)?
Doyou  wan t in teg r at i onwi t h O u t look/Exchange?Do you wan ta  v endor-supp o rte dsolutio n, or a re yo u  comfor table wit h a moreDI Y ap p r oac h?
What fe atures d o you wan t  on y o ur  phon es(voice ,vid eo, m ultipl e  li nes,colorsc reens,  etc. )How much  are you willing to spe nd?

S ome o f t he otherpoi n tsyou bring  up: 
QOS
Depen din g o n you r n e twork  you wi lln eed t o im p lement so m ekin d of  QoS (inter n a l lyand/o r e x ternal ly)to ensure that VO I P traffic isn' t de l a yed  (l a tenc y/ jitter is a KI LLE R) . Infrastr uc ture
Many ( if not m os t ) VOI P phon es hav e a bui l t -i n  pass- thro ugh  switch a ndsu p port VL AN  t a gging,  so
 money_and get_many more features. _
I am_noticing_that all_of_the features of_these systems require_add on licences. _I have heard_of_Asterisk, and see that it's implemented in both Zentyal and Clearos.  I am_a_capable Linux_admin,_but_I know next to nothing_about voip.  
So, I_am looking_for sound advice from people who know their_stuff_and/or have been_in the same place and found/installed a FOSS solution_that worked.  What hardware recommendations_are there? _What_is_the best way to_handle QOS?  Do we need_seperate network runs to each phone_and computer, or can there be one_network run to each station with_a l2 switch and have_QOS handled_at the backbone switch? 
My_current network: 
-We_will be_getting a new_EOC (ethernet over copper) line installed_with 5 mpbs_up/down within a month.
-We have all_unmanaged_netgear switches, and_will_be_separately upgrading_to a pfsense_based_firewall to_connect_WAN to LAN.  We will_be_upgrading to whatever managed switch for the_backbone is decided to_be_adequate.
-There are about 30_user computers total, with 5_servers.  Three servers running debian_linux and_two running_Windows server 2003.  

A:

ServerFault doesn't really do shopping advice -_you need to consult with vendors_and decide what system_works best_for_you.
Some points to_consider:

Do_you want_a fully VOIP system (IP within the_office, your_PBX connects via VOIP to a_provider that connects you_to_the PSTN), or a hybrid system_(IP within the office, and your_PBX connects to the PSTN_directly)?
Do_you_want integration with Outlook/Exchange?
Do you_want a vendor-supported solution, or are_you comfortable with_a more DIY approach?
What features do you_want_on your phones (voice, video, multiple_lines,_color screens, etc.)
How much are you_willing_to_spend?

Some of the other points_you bring up:
QOS
Depending on your network_you will need to implement some kind of QoS_(internally and/or externally)_to ensure that VOIP traffic_isn't_delayed_(latency/jitter is a KILLER).
Infrastructure
Many (if not most) VOIP phones have_a built-in_pass-through switch and_support VLAN tagging, so