FYI: Its not legal in the UK... from our current NOTAM series:
FREQ 123.45MHZ NOT TO BE USED AS AN AIR TO AIR COMM CHANNEL WITHIN RANGE OF ANY VHF GROUND STATION IN UK FIRS FROM:17 JAN 2003 15:17 TO:PERM B0148/03
No other "chat" frequency is provided here, and "numbers" is strictly for oceanic use, according to CAA here. Its a major pain not to have it, and there are efforts to lobby for it
AFAIK, but bearing this in mind it seems you might like to consider discouraging abuse of this privelege where you have it lest you lose it!?
Andy
Buckinghamshire, UK