MacNN noted in a recent post that AT&T is listing the iPhone as having a 1.4 Mbps connection (down-stream) while other 3G phones such as the Motorola Q have upwards of 3.6 Mbps connections. If you are thinking that this is a typo on AT&T's website, think again, because it was also mentioned in their press release about the iPhone (PDF link).
The mobile phones, of course, have a slower connection compared to the 3G cards that AT&T offers. Some of the 3G cards can connect as fast as 7.2 Mbps down. So while Apple is touting their "3G speeds approaching WiFi speeds" you have to wonder why is AT&T limiting the bandwidth on the iPhone 3G so much.
Update: MacNN updated their post shortly after this posting. MacNN's sources are saying that the 1.4 Mbps speed is "observed" speed over the network.