Hi Katti
Unlocking only applies to the telephone network the ipad is aligned to (if it comes with 3G). If the ipad is wifi only this is totally separate to the telephone network and no, you don't need to have it "unlocked".
Would you want to make calls on the ipad? You can use skype via wifi (I do on my iphone and its great - there is a dedicated skype app for the iphone / ipad) so if you have a already have mobile etc for normal calls I don't see compelling reasons to get the 3G version (although of course you may have a reason to do so).
This answer is based on an Australian perspective but I don't see how it could be any different with an ipad from the US. I am sure I will be corrected if wrong!
Exciting!
Joscelyn