Apple has posted several job opportunities on it's employment site seeking individuals with experience with advanced 3G telephony technologies.
Apple is looking for a lab tester and analyst who have experience with HSDPA and HSUPA (High Speed Downlink/Uplink Packet Access). The two technologies are commonly placed under the 3.5G technology umbrella whereas the current UMTS technology used in the current iPhone falls under just 3G.
The implementation of HSDPA and HSUPA in the iPhone would mean significantly increased speeds with HSDPA being able to offer up to 14MBit/s download and HSUPA having upload speeds of 5.76MBit/s. As with current UMTS implementations real-world speeds are no where near what the technologies can deliver.
Back in 2007 World of Apple wrote a detailed article on telephony technologies currently in use in the UK.