Before we had EU-wide free instant money transfers that only worked within some banks. Two guys, who were at one such bank, decided to use it as an instant messenger. So they sent hundreds of messages while transferring just one Cent back and forth.

Until they got a message from a bank teller that they were equally amused by their jokes but should tone down the frequency because every money transfer cost the bank 11 Cents (don't remember the real number, but it was ridiculously high).