If you're stupid enough to post someone's name/contact information/d0cs as well as pranks of them, and the person were to find it, they could contact your host/police/etc. Most people just threaten and never do anything about it, but Phonebomb got shut down for posting names and numbers, didn't they? The pranks themselves are illegal, depending on the state, since some states do have laws against recording phone calls.
As long as you aren't a dick, take names out of your pranks, and don't repost phone numbers/contact inf0s, you should be good, even if it isn't completely legal.