My favorite was back in the days when you actually had to pay per-minute for long distance voice calls. AT&T, MCI, and Sprint would send out paper checks - $50, $75, even $100 on occasion.

You cash the check, you give the company the right to execute a PIC change on your behalf, switching you to their ripoff LD plan. The beauty was that sometimes I'd take two or three checks to the bank at the same time. Whoever processed their PIC change the slowest won, I guess...

Within a year or two, the checks dried up. I can only assume that they all blackballed me from outright cash offers. So then I ran through 2-3 years of FF mile promotions. Then came voice-over-IP and wireless phones with unlimited LD, and the fun & games all came to an end...