Alright, so the iPhone 3GS supports HSDPA (High-Speed Download Packet Access) which everyone with a 3GS has seen and loved. Well the iPhone 4 supports HSUPA (also known as Enhanced Uplink) which provides a much improved upload speed averaging around 5.76 Mbps.
However, if you’re with AT&T or some other provides that don’t support HSUPA, then you will not see an improvment.
Jobs: That’s ‘theoretically’ because the carriers don’t support it yet
In the US, AT&T’s 3G HSDPA primarily maxes out at 3.2 Mbps, with typical speeds ranging from 0.7 to 1.7 Mbps. The company is in the process of deploying faster 7.2 Mbps service, but this is currently limited to just a few cities: Charlotte, Chicago, Dallas, Houston, and Los Angeles and Miami.
In terms of uploads, AT&T’s 3G HSUPA network operates with typical speeds ranging from 0.5 to 1.2 Mbps, roughly two to four times faster than 0.3 Mbps theoretical maximum of the non-HSUPA capable iPhone 3GS. Not all of AT&T’s 3G network supports faster HSUPA service.
Outside the US, several mobile operators in Canada, Europe, Asia, and Australia have been supporting 7.2 Mbps or faster HSDPA for more than a year (with some offering even faster 14.4 Mbps or better service) and 1.4 to 5.8 Mbps HSUPA speeds. Even faster HSPA+ networks have started offering 21.6 Mbps downloads over the past year.
Here is a comparison to the 3.5G HSDPA/HSUPA on the iPhone 4G and the Wireless N Speeds (802.11n).
It would be very interesting to find out what Rogers/Telus are supporting on their towers. I haven’t had many issues with download or upload speeds.
Source: Appleinsider.com