Ah the good old days, when moving up from 110 to 300 to 1200 was so amazing. I remember kicking off the download of a large photo from CompuServer at midnight, and then going to sleep, since it would take about an hour to get a single picture. Now it takes one second.When the internet was fairly new we had one of the first internet T1's in the area.
Your phone only uses one download frequency.The fastest EDGE based smartphone to date was capable of 4 channels at 56kbps over EDGE which gave a maximum of 224Kbps, BUT the true theoretical maximum for EDGE is 8 channels for a total of 448kbps.
Who knows what iPhone is capable of? Does anyone know how many channels in the iPhone EDGE radio?
The way EDGE works is this: there are 8 time slots per frequency. Four can be used to download to you, one can be used for upload packets, four are dedicated voice only.
Each slot is capable of a 59kbps burst. So if you're the only data user on that channel, you can get 4 slots x 59k = 236k. If there are more users, the slots are first-come, first-served for download. Uploads are collision-based, and degrade quickly. Since web browsing is over TCP/IP, there has to be lots of handshaking, and multiple users can cause a slowdown to far less than 59k per user.
Rumor is that Cingular, in some areas, is taking one or more of the voice slots and reallocating it to data to try to boost internet access. (More dropped voice calls.)
Basically, the more people who buy an iPhone in your area, the worse your net experience will be. So try to dissuade your friends.