Did a speed test with the Speedtest app on an AT&T iPhone 4 and the TB just for the hell of it.
Hollywood, CA
iPhone 4. 3G and 5 full bars
.48 Mbps down
.22 Mbps up
TB. 4G and 4 full bars
10.35 Mbps down
29.78 Mbps up
Right there is one reason I'm dumping my AT&T iPhone 4.
Did another test using the TB wifi hotspot and connected the iPhone 4 to it. When connected over wifi to the TB, the iPhone 4 got:
4.21 Mbps down
9.04 Mbps up
4G all the way!