Whilst painfully waiting for my n900 to arrive, I've been looking around for a good sim only contract.

The best one for me (UK) seems to be with O2, which works out at about 20 GBP a month:

Online simplicity 20 SIM Only
Pay Monthly contract
1200 texts / 600 mins
Includes Unlimited Web Bolt On

Apparently the Web Bolt on has no caps etc. and is fine as long as you don't tether the device.

Anyone got any advice on this?