Certain prank phone calls can be funny indeed. I grew up listening to the Jerky Boys, and enjoyed some of their tapes quite a bit. Doing the pranks myself? Never my style personally. I really don't take enjoyment disrupting someone elses day, and wasting some of my own, for some foolish fun. To each his own.
PS: I would reccomend that if you have a NEED to prank, leave it to businesses, and good natured fun. Causing a potential disruption in someones relationship or marriage sucks. Whether or not the spouse involved believes you or not, you can seriously dent a relationship between two people who formerly may have not had a problem. Just a thought.