Here is a very funny prank.
Step 1: What You Need.
1x Deck of Cards.
1x Friend with a sense of humor.
Step 2: The Prank
All you do is tell your friend to pick any card. When he does that tell him to call a random number and ask what his card is.
Step 3: The Prestige.
If it goes right he will call an absolute stranger and they'll wonder what on earth he is talking about.