I feel the same about Google Voice at the moment. It's killer feature for me right now is the ability to text and call people from my Google Voice account from OS X. I use GrowlVoice[1] extensively. It's easily one of my favourite menubar applications.

If TextSecure could replace this functionality it'd cause me to seriously reconsider GV

[1] - https://itunes.apple.com/us/app/growlvoice-google-voice-clie...