I can see two perspectives on this:
1. I prefer SIP phones or SIP/DECT phones as they are often more capable than an analog phone paired with an ATA.
»www.mgraves.org/2008/10/cordless ··· ess-ata/
2. There may be cases where you need to leverage existing analog gear
»www.mgraves.org/2008/10/small-of ··· e-cheap/--