DO NOT JAILBREAK! it wont ruin it but you dont get your warrenty. Just buy a $25 sim card. I think it is called a stealth sim card. its not that expensive and you dont risk messing up your iphone.

Good luck

Here is the site,

Don’t worry though if you fallow the direction you’ll do just fine.
I’ve done it through this exact guide.

Just in case you have to take it in, just simply do a restore and your iPhone is as before, as if it never happened.

Enjoy a much freer iPhone.

Hope I’ve helped.
- John.