General rule: It's only a platform for whoever gets to decide what runs on it. Right now, it sounds like it is either Danger's platform or T-Mobile's platform, but it's not the end user's platform.

If data 'overuse' is a problem, then they should just charge for the data. Pick a $/megabit and stick with it. If this mucks up your voice model, then pick $/megabit with low latency, and another $/megabit for fewer guarantees. FedEx or second-class mail - but no more. You'll just confuse the end-user.

They might think they want to charge by "what the bits are worth" - but this is dangerous territory. Bits for stock trades may be quite valuable. But bits for my horoscope are worth almost zero. Bits for video are probably worth even less on a per-bit basis. You can only climb up the 'bit value' scale if you are prepared to climb down it as well. It's market pricing, and the market NEVER guarantees to cover your costs.