The best answer I can find is not possible. Though it is technically possible, it's not as simple as flashing the phone. Boost is owned by Sprint and it's doubtful you could find anyone in the company willing and/or able to add the Moments esn to the Boost database. Any way of doing this other than having the esn added to Boosts system would require actions that are dubious and/or illegal and are not for discussion here! Frankly, for a phone as old as the Moment, it just isn't worth it. Sorry!