I was under the impression that the GV client also provides some degree of VoIP client functionality.
It would be hard to see what is controversial about this proposal if that weren't present. What, is AT&T complaining about more subscription minutes being used?
AT&T is freaked the fuck out because your Google Voice number is actually portable to any carrier, completely dynamically, in perpetuity.
Number portability in the US as it is now only works if your new billing address is in the same zip code as your old number, and usually doesn't work at all when you're trying to port out of a VoIP provider or in to a PoTS line.
Really? I ported an Atlanta number from T-Mobile to Sprint without a single problem here in Seattle. They did ask me for an Atlanta zip code during the process, but it never came up as an issue.
Phone number portability (one carrier to another) is mandated by law. They gave you no problems because they mustn't. GV style portability (a virtual number that works with any carrier) enjoys no such privilege, so they can, and in Apple/AT&T's case, have, blocked it.
It's not "a virtual number that works with any carrier." I can assure you that the number is (1) natively homed or (2) ported - to a particular physical, facilities-based carrier (generally a CLEC) at any time. In a lot of places, Google Voice is using bandwidth.com's new CLEC license holdings (after they stopped being a pure Level3 reseller), and probably the usual national-level multibillion dollar folks that are interconnected to everyone, everywhere and have a lot of direct end-office trunking: Global Crossing, XO, Level3, etc.
For example, here in Atlanta, my friend has a Google Voice number out of 404-939. If you take a look at the pooling and/or NANPA assignment information for that block, you'll find it's pooled and held by bandwidth.com's new CLEC:
No, Apple / AT&T is concern about competition and letting their customers easily move between carriers, as GV permits a single portable phone number, messaging, etc.
It would be hard to see what is controversial about this proposal if that weren't present. What, is AT&T complaining about more subscription minutes being used?