Personally, I'm not going to pay $30/month for AT&T 3G.
As long as Tesla allows the car to connect through my phone and through my home router, I'm not going to be upset about it.
In fact, I imagine that's why Tesla hasn't announced anything, yet. They haven't been able to work on the connectivity stuff because they've been busy trying to work on the vampire load / clean wake up stuff. and until they can offer a connectivity option that isn't $30/month through AT&T, they know that they can't charge us without us getting pissy.
My iPhone is AT&T, but I might switch over to Verizon once they allow tethering. As it is, the Google maps view is typically about half empty as it can't update fast enough while I'm driving. I live in San Jose (10th biggest city in the country, and part of Silicon Valley), so there's really no excuse for poor coverage.