I once did this very thing, with the added feature of being able to send messages to either user (masquerading as the other). It was fun as a proof of concept and as a way for me to learn Python Twisted, but using this technique for an extended length of time is a bad idea for various reasons.

Edit: one example of things going bad for you:

Stranger 1: 13/f/fl, u?

Stranger 2: 18/m/NY. Can I send u pics?

Congrats, your IP is a couple of bad decisions away from committing a felony.