iPhone Upgrade on O2

Hopefully an easy on for someone.....

My girlfriend is eligible for an upgrade on O2, 4 months ahead of me, and bless her she's said she'll upgrade to an iPhone and let me have it.

Is this going to work? Is there anything that ties the phone to her SIM? Would prefer not to have to jailbreak it at the minute. If I slot my O2 SIM in, will I still get the free web browsing etc?

Thanks

I am not 100% on this but,

Because she is activating the phone on her account, she will have the data plan on her account. If I'm not mistaken, the data plan must remain on her account until for a certain period of time before it can be removed/canceled.

So basically, you can put your SIM in there, add a 3G data plan, but you will be paying monthly for both you and your sister's lines.

You won't get "free" web browsing unless you have a data plan on your account.