The answer is simple. No. The only sim cards that can be used in an AT&T cell phone have to be AT&T. Any other kind of sim card will not work. To use a boost mobile sim card, the phone has to be bought from a Boost mobile store or from the boost mobile online website.
In order to use a Boost Mobile Sim card with an AT&T phone you must first unlock the phone. Some models have information on the internet on how to do this. The iPhone is the best phone to use though if you are using another carrier because so many people have already unlocked them.