I do not know when and where, but a few days ago I read a note that said "what if Google starts allowing phone calls among Android devices?". Yep, phone calls over IP, completely around the carriers. No voice dollars to the operators. Same as Skype on your PC, but your PC is actually mobile and you can move it close to your ear (try that with an iPad).
Well, no voice revenues anymore. That might hurt an operator, in particular in the US where the data plans are unlimited. And hurt a lot.
What prevents this scenario to become real?
The network. The bandwidth is not there yet. The network is overloaded. If you try a VOIP call on a mobile device, even with 3G, the quality is horrible. It is like trying Skype on a modem (I did, do not try, it is not good).
Now a thought: what can the carrier do to prevent this scenario? Simple, they can just keep the network as it is today: not-good-enough. They can make it better but still not good enough, because the amount of data load will increase naturally.
Think about it: they have to invest gazillions to improve the network and the only benefit of it might be having Google wipe them out. Does it make sense to you? Would they do it just because the users are asking for it? Can the market push it?
I really hope so. I would hate to see the networks crippled just for carriers to prevent the inevitable.
However, I actually see a good reason for the carriers to prefer the network to be crap.
And that is not a good thing.