Is there anything that could be legally done about this?

My boyfriend has been a dispute with 2 guys over the past few years. He has done nothing wrong to either of them, but they do everything in the world to slander him, frame him for things he isn't doing, and try to turn all his close friends, and me, against him. Well, one of these guys is really good at computer hacking and such, and is somehow using my boyfriend's cell number to send pictures of...well, male genitalia, to a bunch of random girls. My boyfriend isn't sending these pictures. They're not from his phone, and they aren't even pictures of him. These girls are about 15, 16, 17 and he is 20, so this could cause some serious problems. For one, how would some one be able to use his phone number and make it look like he were sending them? He even got on Verizon where they log all your texts and stuff (which I know nothing about...I have AT&T) and they hadn't come up as being sent from his phone. And second, is there any kind of legal action that he could take against the guy that is using his number to send these pictures? My boyfriend is going to change his number, but for now, it looks like he is being a huge pervert sending pictures of his junk to underage girls. Is there anything that can be done about this before he is wrongly accused of being a sex offender? :P