▁launched ▁in ▁ 2 0 0 5 ▁in ▁select ▁mark ets , ▁and ▁to ▁all ▁of ▁Com cast ' s ▁mark ets ▁in ▁ 2 0 0 6 . ▁Com cast ' s ▁older ▁service , ▁Com cast ▁Digital ▁Phone , ▁continued ▁to ▁offer ▁service ▁for ▁a ▁brief ▁period , ▁until ▁Com cast ▁shut ▁it ▁down ▁around ▁late ▁ 2 0 0 7 . ▁In ▁ 2 0 0 9 , ▁after ▁comple ting ▁transition ▁from ▁their ▁old ▁service , ▁Com cast ▁had ▁ 7 . 6 ▁million ▁voice ▁customers . ▁As ▁of ▁the ▁end ▁of ▁ 2 0 1 3 , ▁Com cast ▁Digital ▁Vo ice ▁had ▁reached ▁ 1 0 . 7 ▁million ▁subscri bers . ▁ ▁At ▁the ▁start ▁of ▁ 2 0 1 2 , ▁Com cast ▁stood ▁as ▁the ▁United ▁States ' ▁third - larg est ▁resident ial ▁tele phone ▁provider . ▁At ▁that ▁time ▁the ▁company ▁supplied ▁ 9 . 3 4 ▁million ▁resident ial ▁tele phone ▁lines . ▁ ▁X fin ity ▁Vo ice ▁allows ▁communication ▁over ▁the ▁internet ▁using ▁Vo IP , ▁but ▁uses ▁a ▁private ▁network ▁instead ▁of ▁a ▁public ▁IP ▁address , ▁which ▁allows ▁Com cast ▁to ▁prior it ize ▁the ▁voice ▁data ▁during ▁heavy ▁traffic . ▁In ▁technical ▁terms , ▁on ▁Com cast ' s ▁Hy brid ▁F iber ▁Co ax ial ▁network , ▁calls ▁are ▁placed ▁into ▁individual ▁Un sol ic ited ▁Grant ▁Service ▁flows , ▁based ▁on ▁DO CS IS ▁ 1 . 1 ▁Qu ality ▁of ▁service ▁standards .