Good point. This reminds me of the Chinese govt vs Tor IPs. Most governments have nothing close to the systems set up by the Chinese, and even they're having a hard time. It also maybe possible to embarrass them in their favorite UN clubs or the world press if they start blocking numbers. I bet there are ways around the telecom guys stealing bitcoins, too -- anything from a separate one-time password device (could be super simple and cheap, even a printed card, especially because the individual transactions are mostly small) to some security questions, like "what's the 3rd letter of your son's name".
It is a little tougher than Tor, because the mobile network infrastructure is more centralized than the internet. Still, all we need is one partner willing to work with us (and get paid messaging fees), and we're in.
The security measures described are all possible, for sure. Ideally, the system should be able to function only on SMS commands, since many users will not have a mailing address or second device. Still, secondary security measures can be implemented, such as a pin number.