Can I unlock an AT&T's Iphone 5 to Sprint?

I found an AT&T Iphone 5, can i unlock it to make it run on Sprint's network?

AT&T uses microsim cards and I don't know if sprint has those.

AT&T is a GSM Network Provider, and uses Sim Cards. The iPhone 5 uses micro-sims.
Sprint is a CDMA Network Provider. It neither uses sim cards nor any other external factor. It is linked with the network.a GSM phone can't function on a CDMA Network.

AT&T is a GSM network operator whereas Sprint is a CDMA network operator. You can't unlock a GSM network unlocked device with a CDMA operator.
Anyway, If you still need to unlock your AT&T network locked iPhone 5, You can do it using remote unlocking service. You can get the remote unlocking service for an iPhone 5 from http://www.simpleunlocking.com/apple-iphone-5/rs16wp9/ This method of unlocking is safe, simple, affordable and quick. This method of unlocking doesn't require a jailbreak too.

Yes you can unlock the at&t iPhone 5 and just because Sprint is releasing their iPhone's as CDMA does not mean that you can't take over your iPhone to them, they will find a suitable sim for you - don't believe me? A simple call to Sprint customer care will resolve your question. Best place to unlock your at&t iPhone is http://unlocksexpress.com/ it will be done within 24 hours and cost only $4 bucks.