The thing about an awful lot of modern comms tech is that it's built around the idea of avoiding single points of failure/loss of data throughput.
I've no doubt that criminally minded types were using their mobile phones to co-ordinate efforts during the riots - as they probably do even when there's *not* rioting going on. They probably also used mobile web access, mobile email access, Blackberry messaging, texting, and god knows what else. I read some reports claiming that some gangs were co-ordinating their efforts through young lads on bikes acting as messengers.
BT still have payphones in some areas, though they're getting rarer. Plenty of coffeeshops (and other businesses) offer free wireless, and some of it's still open-access. So effectively shutting down the kind of communication access that's being discussed here is not as simple as pushing some digital equivalent of a Big Red Button for certain services.
At issue is the idea that the rioting was aided significantly by this communications tech - but what we've seen doesn't really confirm or deny that. There's no real evidence to suggest that *without* access to said tech, those rioting wouldn't just have smashed things up anyway (but in a less organised manner).
This smacks a bit too much of a knee-jerk "LOOK, WE'RE DOING SOMETHING" response, and not enough like a "We've considered the circumstances and formed a rational response in the event of recurrence" response. I'm always unnerved by this sort of rush to action because it suggests that we might get yet more crap, poorly-worded legislation that can then be misused by prosecutors.