is it possible for my iphone 4s from sprint to be unlocked for t-mobile?

[Beniia]

So I bought an amazing Iphone 4s off craigslist, which was used by sprint or cricket and the seller told me to go to t-mobile and they'll unlock it for me. Is that possible because I saw programs saying they unlock any carrier's iphones for only 20 bucks, plus the iphone 4s iOS of 6 has a sim slot

 

[priyakalai]

So I bought an amazing Iphone 4s off craigslist, which was used by sprint or cricket and the seller told me to go to t-mobile and they'll unlock it for me. Is that possible because I saw programs saying they unlock any carrier's iphones for only 20 bucks, plus the iphone 4s iOS of 6 has a sim slot

ya,it's possible.
If you need to switch your sim card,you will need to unlock your mobile phone.If your iPhone 4s locked to Sprint network,you can easily unlock your iPhone with a help of online unlocking service provider.Nowadays there are lot of online unlocking service providers available.I would suggest you to visit this site Unlocking4u.com Here you can unlock your mobile phone without jailbreaking.Recently i unlocked my sprint locked iphone 4s here.I like their services.