It depends on your situation. If I understand things correctly, and assuming you live in the US, it's probably very useful as you can use it anywhere.
To me, it's a complete waste whenever I'm in mainland Europe. Considering the fact I live there, the 3G is useless (oh, yes, I can visit wikipedia with it, well, hurah).
But on holidays in places like Japan, the UK and the US, it's a lifesaver, as I don't carry a mobile phone that works there.
