Need a dead simple VOIP option for someone that just wants to make calls on their cell -- is Ooma it?

[Buzz]

Remember when GV meant Global Village instead of Google Voice ? ? ?

As Rob'eM says, GV will forward calls seamlessly to a cell #, and the GV 'droid/iOS apps let you make make calls from your cellphone appearing to be from your GV #. There are other VOIP services/apps that can also do this, but to get anything nearly as seamless, you're gonna have to pay for the privilege.
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