Can I factory unlock my iphone in the middle of a contract?

I have an AT&T IPhone 4S. I want to factory unlock it using globalunlocks.com but can I do it when I'm in the middle of my contract? Will it damage delete or alter any parts of my phone? (Settings, apps, contacts, etc.)

Yes you can and no, it won't mess anything on your phone cause whoever is doing it for you
and if they know what they're doing then they should know that is done trough the imei number.
but once you get the green light make sure you back up you phone on iTunes before you restore it