Most of us don't need 802.11N for out iPhones, at least not till we get WiFi syncing and the ability to stream high-bandwidth movies etc.
This is probably good according to a story over on TUAW. They point out that there is very likely no advantage to the 801.11N offered by the iPhone 4, calling it: "802.11n is partly just a marketing bullet point for iPhone 4 instead of a truly beneficial feature."
This is because its limited to 802.11N in 2.5GHZ only, not the wider allocations in the 5GHZ bands. As such, they don't expect anywhere near the speed boost seen by other devices (iPads) using 802.11N which offer 5GHZ as well as 2.5.
They also link to an analysis on ArsTechnica that suggests there are some technical issues with the initial release of the WiFi drivers in the phone 4. The 3GS connected easily to the network at WWDC, but the iPhone 4 could not connect at all till they forced everyone to turn off their MiFi routers.
They expect this will be fixed with a point release reasonably soon, if not already.