How to unlock sprint iphone 5 for att?

I was given a Sprint iPhone 5 but my cell carrier is ATT. How do I unlock the phone to be compatible with ATT. Called sprint but they said they don't condone unlocking so they were no help.

Try to check software and tutorials on the internet on how to unlock your phone. Or you can check on professionals doing an unlock service. I did mine at http://jailbreakhome.com/iphone-factory-unlock, they provide a very affordable unlock service.

First off all, you can't use a Sprint phone with an ATT signal disregard if you're unlocked or not.
The reason why is because they're both running on different signals.

Sprint runs off a CDMA signal while ATT runs of a GSM signal, so even when unlocking your Sprint phone, it won't do you any good.

Your alternatives:
You can post your phone up for trades on craigslist, eBay classified and look for the same model phone which came originally from at&t.
Or simply sell your iPhone 5 and then use that money to purchase an ATT iphone.

You can actually trade the sprint phone for a t-mobile phone because t-mobile also uses a GSM signal, but you must unlock the iphone if it's from t-mobile. Unlocking is easy, doesn't require any knowledge and can be done in 5 minutes. Check the link in the source box
http://www.iphoneunlockinfo.com/methods.php

The link gives you three methods of unlocking, the first one is universal, doesn't require jailbreak and the second one works, but is risky because you might brick your phone if jailbroken wrong.

If you feel a little sketchy about the first method, think of it like this, if an eBay seller was scamming their customers, the big eBay coperation would've cracked them down already and banned them from the site. They also have a eBay protection policy and you're not loosing much. First method definitely works because i've used it and learned frome xperience, but you have to give trust to earn trust.