like said above, theres a new iPhone software coming out in June. It will be a free upgrade, so if you buy your phone now you'll be able to get it.
There are rumors of a new hardware device in 2Q. But no one knows if this is true or what it will have. But probably 3g..
Its a great phone and I wouldn't wait for something else to come out. If you always wait for new tech before you buy, you'll never buy anything.