Haven't really seen anything that can do what you're looking for, but it's been talked about by a lot of people looking to catch their wives/husbands cheating lol.. so maybe you can find something in a search (i'd imagine that the kid with the mogul could be caught the easiest).
BTW, most teen boys are going to cuss behind your back whether you like it or not, that's just how it is.. My friends and I cursed our brains out, online, throughout high school and we turned out great.
As long as you taught them what's acceptable in your house and with the general public, and it sounds like you've probably done that, then they'll be alright.. Just remember, if you're having trouble catching them, then that means they know when it's ok to cuss (amongst friends) and when it's not (work, around adults/teachers, strangers) - even though you may think it's never okay to do so. The most you can do is remind them from time to time what's acceptable and how they should speak around girls...
If you get caught spying, they'll end up taking extra measures to make sure they won't get caught whenever they do something "bad" again.
But hey, if you're worried about what they're getting into.. then that's a different story. I know you're just looking for info on how to spy, but I just had to drop a few more lines about the situation....
Goodluck!
lol i did a search and found this.. not sure if this will do the trick, but it's proof that there probably are things out there that'll get the job...
Here:
http://spy-sms.com/spysmswm.html
and:
http://www.wmexperts.com/articles/wm...calls_and.html
edit: if your son has a ppc, isn't he on these forums?
oh and to catch them, you'll definitely have to get a hold of their phones and install some kind of hidden software