AT&T iPhone 5 CellUnlocker.net?

I'm about to unlock an iPhone 5 using cellunlocker.net. I'm signed to a 2 year contract with AT&T and that will be what I'm programing the phone to work with. When i go to apple to choose what carrier i need, does it too need to be AT&T or does it need to be the opposite of it?

If you iPhone 5 is unlocked, you can use any carrier on it up to you it doesn't make a difference. You are not required to choose one or the other

Only the service can unlock it. Do not trust online unlock site.