If I am not mistaken it is called iPhone 4G at the moment because it is iPhone Fourth Generation.

It got nothing to do with your 3G Broadband or 4G Broadband.

A lot of people mistaken that iPhone 3G means, iPhone made to run 3G internet. It is the 3rd Generation of iPhone, hence called 3G.

So the new iPhone would be the 4th Generation which currently being called iPhone 4G until there is official name for it.

So it doesn't means that it has to run in 4G broadband.

iPhone 3G/4G indicate the phone's generation.
3G/4G broadband indicate the technology of broadband.

Both are different thing.

Correct me if I am wrong.