My understanding was that the iPhone (unlike evey other GSM phone I know) does not use a SIM card. So even a jail-broken iPhone (presumably set to run on T-Mobile here) could surely not be used on another (ubiquitous) GSM network in Europe (where I have purchased a SIM card for as little as about $10 to cover a few weeks in a country) without being re-jailbroken? Unless something has changed, there is nowhere to plug in such a card, as far as I know