The tower itself, no.
The outbound pipe from the tower to the CO/next hop, maybe.
It's not uncommon to see a T1 or two supplying a whole tower's worth of users. Generally high contention ratios are fine -- the high latency of mobile data lets you pull some clever QoS tricks, and the usual usage patterns of mobile data users (light browsing, some e-mail here and there) mean that you don't really have to worry to much about being over-committed.
That is, until some guy decides he's going to "stick it to the man" by convincing loads of folks to stream relatively-high-bandwidth video over UMTS/HSDPA. If you've only got 3mbit on the backhaul, all that's needed is 5 smug pricks streaming video before you make the experience suck mightily for everyone on that tower.
So please: don't. You won't "stick it to the man". You won't prove anything to AT&T. They won't even notice. What you will do is help ensure that everyone on the same tower as you has higher latencies, lower throughputs, and an all-around worse experience than they otherwise would.
In summary: don't be "that guy".
How are apps such as Youtube, Orb and Simplify Media any different then Sling? My point is that it is ridiculous that because of AT&T being worried about their network which is supposedly the "fastest" 3G network in the US, they decide to ban a program that uses the same amount of network connection of others one that are available. It's ludicrous.