Slight OT, but FWIW in the US I've not had a problem using an AT&T GoPhone SIM with the $20 / 100MB MEdia Net data pack. I know they recently changed their 'policy' so you couldn't use these packs with a non-AT&T iPhone (bit silly really), but I believe there is a workaround (
drewbles can correct me if I'm wrong / miss anything):
- Buy a GoPhone SIM at a convenience store, or at worst an AT&T store (and do not mention that you have an iPhone)
- Buy some recharge credit (if you want data, get more than $20 - I believe you get bonuses / better rates at $30/$50 recharges)
- Activate your SIM on the phone or online, then register your SIM on AT&T's website (without giving them your phone's IMEI code if they ask) and add the data pack
- Use this program (Unlockit - APN Changer for your iPhone) to change the iPhone's APN to the one AT&T uses for GoPhone, so you can actually use the data
It seems like a lot, but it's actually pretty straightforward, and the payoff of being able to use your iPhone unhindered is definitely worth it.