Like Brad said simple judgement will keep you out of trouble. If the person is laughing along with it go ahead. But if the person gets angry don't call again. I simply place all my calls through the operator to a calling card. It cost me $.75 everytime, though. I also can spoof my caller id which can be fun. Get a free k7 voicemail account and spoof your number to it and call people without blocking it saying
"Hi, this is Dr. Jackson, the president, the CEO of the Shady Side Locals. Don't have a gang? No problem! With your low monthy payment of $29.99 you can enjoy all the benifits of being a gang member."