"Bandwidth is a limited resource and 3 would much prefer to support 200 users on a cell with only a few hundred kilobits each, than 20 users downloading video files while the rest can't get at their email - though the 20 users concerned might not feel the same way."
In your dreams... A 21Mbps sector has less than 2Mbps average throughput, and there are up to 3 sectors to a cell typically..
You would be lucky to have 2 sector users able to stream YouTube at once. That's 6 cell users.
3G/HSDPA is rubbish.
It uses CDMA, so fully loaded the range shrinks and available total capacity can be 1/4 as much.
They need to do this and have < 1G caps or it is worse than Dialup. In Ireland due to mad expensive line rental (26 Euro) and poor BB availability they sell this as a fixed solution. Fixed users are online longer than Mobile, so even if many "mobile" are mostly fixed, 3's own assertion that 50% of users are "fixed" makes system 5 times slower than it would be for only mobile users...
See why 3G is poor and Mobile can't Deliver Broadband. True Fixed Wireless can as it is x16 better in the same spectrum:
Midband Forum. Clue. What's not Dialup but worse than Broadband?