Using US iPhone 2G Unlocked in UK/Italy?

There is no such thing as an unlocked US Original iPhone. ATT does not unlock them.

In other words, you hacked it which means no one here can help you but Google is your friend for this sort of thing.

Lets pretend that the words AT&T and US are not in this post, and the comment "I unlocked it" was not there either. It's Friday and I feel like being mildly helpful today...

Lets say you had an original iPhone that had been officially unlocked (which could happen in the UK, if the original service provider had unlocked it), then you could theoretically use any compatible GSM carrier world wide.

So for the original iPhone it is a Quad-band GSM (850, 900, 1800, 1900, MHz), if you find a compatible carrier then a sim card should work when placed in the iPhone. Keep in mind that the iPhone will try to use data, and could go through the pay-as-you go credits rather quickly if it is not disabled. In the older iPhone firmwares there is no cellular data toggle like there is in iOS4.x.

I know someone who has an old 2g that he bought second-hand unlocked with firmware 3.1.3 on it to use purely when travelling so that she was not tied to her network supplied phone.

She has used it in the UK and other parts of Europe using a local Vodaphone PAYG sim and apparently without any problems. In Europe nearly all of the carriers do a PAYG or monthly contract service.

I also warned her about the data roaming costs but it appears that with the 3.1.3 there is an option on the 2g to switch data roaming off.