OK, I know this might not appeal to everyone because its 3 Mobile, but its FREE after all:
Get a FREE 3 SIM card with -
£10 Airtime Credit
150 MB of data
FREE 3 to 3 mobile calls (unlimited with fair usage)
FREE Skype calls
FREE Internet/MSN Messenger (if you phone supports this)
You have to have a 3 mobile or an unlocked phone. However I think this is pretty useful, even as a secondary phone number. You certainly can't knock being given £10 of calls, 300 texts and 150MB data for free. Once you have used up your allowance, just throw the SIM away if you don't want to pay anything more! Just follow the simple instructions to get the SIM sent to you.
Please don't freeze this out just cos you hate 3 - someone might find it useful.