I think its Google Voice, except that Apple so far seems to have decided not to swoop in and kill it.  I feel (especially since it is clearly getting attention) that it could get killed.  But then there is this other side of me that wonders... what if Jobs personally let this stick around just to totally f*** Google on Google Voice.  The "rivalry" between Apple and Google seems has reached a fever pitch (possibly just in the imagination of the press) and would'nt it be fun to think that Jobs is sitting there saying "I'm going to let this one ride just because its NOT Google".

If that or something like it were the case, it could also be a signal of a power shift between AT&T and Apple.  Early on there was no way that AT&T would want to have a phone that allowed you to avoid paying AT&T money.  Nowadays maybe AT&T will go with the flow (a.k.a. whatever Steve wants) to try and keep exclusivity with the iPhone 4.0 release.  

Will I use it?  Probably not.    And I have to pay another $15 for this service on top of the money I already give to AT&T?  At least Google Voice is 'free'.  Who wants to talk on the phone anyhow?  I'd consider getting a MMS only plan