FaceTime stopped working?

I've started having problems with FaceTime with another friend ... (wireless of course since that's the only way FaceTime works). We've had FaceTime working fine for a few weeks until my friend changed his router ... so I'm assuming there is something in the router that might be "blocking" FaceTime ... just an assumption. He successfully browses the web and does other activity via his wireless connection (via his iPhone 4S) to his router.

So my question, is there anything that needs to be set in his router (such as open ports or something else) to allow FaceTime to work?

We both have an iPhone 4S, he is AT&T and I'm Sprint -- but like I said "I think" the problem is his new router since that's when FaceTime stopped working.

He's check the FactTime settings (On and AppleID setup) and his wireless connection to his router is working.

Any hints what to check next to get FaceTime to work?

Thanks, Rob.