for htc desire s: how to know your phone's region? i'd like to update my software from gingerbread to ICS, just want to make sure to get the right update for my phone.
You must have been confused by seeing too many files for the update. Actually there is only one file to update to ICS and hence it is the right file. The file is RUU, i.e. ROM Update Utility.

So from, http://www.htcdev.com/devcenter/downloads 

Download


  Desire S  HTC  WWE  RUU  N/A  v4.0  404.0 MB  14.01.401.2


And yes the region is WWE for this case.