No, you do not have to port your number (though you will get an option of also having a google voice number). You essentially set up your phone to forward to google voice, then it will act as your voice mail provider and you can then have google voice notify you of new voice mails, read transcriptions of the voice mails (albeit sometimes not the best transcriptions) and listen to them from the app, or from the call log (if you opt to integrate it into your call log). There is a widget that allows you to review your voicemails from the homescreen. And if you happen to be nowhere near your phone, you can always go to the google voice website to check your voice mail. I hear tell this will eventually be integrated into hangouts, so it probably wouldn't make much sense to use it for text messaging at this point in time since hangouts is already doing that.
I use the att visual voicemail app. Doesn't require me to use there texting app.
Posted via Android Central App
Interesting. If I designate the ATT app as my messaging app (first), then try to open another messenger app, the phone will always ask if I want to change the default messaging app. Do you experience this or are you not being asked?