Do I need to jailbreak my IPhone for o2 Simplicity?

I have just bought a new IPhone 3G off eBay which was an unwanted upgrade for someone. I have also signed up for an o2 Simplicity contract.

My question is, can I fire the sim into the new phone and register in ITunes without any problems or am I going to have to jailbreak the phone to use this sim card? or Perhaps should i register the phone with a PAYG sim and then use the Simplicity sim after or is this even possible?

I want to keep the phones Warrenty

So it should be good to register with that sim through ITunes?

Thanks for the advice guys! Just for anyone elses future reference, worked fine!