Which softphone are you using? Might be able to help with that as I've worked with a few, not with TekTalk but should be the same.
Well, he said the softphone can work with TS, but we were only talking in the context of some android app...so getting the android app to work like a softphone is the trick (as long as Ma Bell and TS both cooperate)
Have you disconnected your ATA? Your cell phone cannot be connected to your SIP account while the ATA is active.