I personally hate phone pranks on the radio. They're usually mean-spirited or gross or funny only to the person doing them, the victim's response is rarely funny in itself. But I like the phone scams they do on 104.7, because they let the victim know it was a scam in the end, and they usually aren't mean-spirited or hurt the victim.
Fortunately for those who can't listen to them at 7 o'clock in the morning, a bunch of them are online at Kid and Ruben's website. My current favorite is one where they pretend to be holding a guy's wallet hostage. The altered voice was a nice touch.