It's a great phone. Probably not the best decision considering the iPhone 5 is rumored to be less than two months away. It'll probably cost the same as what you paid right now for your 4. $199, or $299 or something.
Rumor has it that it'll have both CDMA and GSM radios in it so you can buy it anywhere in the world and unlock it anywhere in the world with no restrictions. If that's true, that means you will be able to get mobile data anywhere as well. As of right now, iPhone users can't always get data in other countries because of the bands not being supported. They do get voice and text, however.
Masta might check if what I said is true. I think it is, but remember, what I stated is what is rumored. But if it were to be true, I believe these to be the implications.