Which software/website should I use to factory unlock my AT&T iPhone 4S?

I need to unlock it to be used on T-Mobile. I want a permanent unlock and I was wondering if any of you have done it and what your suggestions are?

Use Remote unlocking method to unlock your iPhone 4s. It is more secure than other unlocking methods. It gives permanent unlock solution to your iPhone 4s. You can get it from any of the online service providers like http://www.theunlockspot.com/apple-iphone-4s/rs16wp9/ to unlock your iPhone 4s from AT&T. After unlocking your iPhone 4s, you can use it with T-mobile and any other GSM carriers.