Until now, there has been little evidence that Apple intends to release a 3G version of the iPhone, though it has long been hoped for. Over the weekend, there were several sightings of T-Mobile advertisements in Germany for the iPhone, and included in the spec list is HSDPA 3G and storage capacity that is beefed up to 16GB. Whether or not these ads are PhotoShop trickery or genuine is unknown.
Either way, Apple would likely not license 3G technology if it didn't plan to use it...at some point.
When exactly that will be is anyone's guess.