Yes I assume you could if AT & T do pay and go sim's ( it's called prepaid in the US).

You will get calls and texts only and if the Bold has wifi you can browse with that.

Bear in mind that it may be cheaper to get it unlocked in the US, AT & T may even give you the unlock code if you ask nicely. You can still use the AT & T sim when it is unlocked.

Then when you return home, get the Blackberry package, sweet