Based on your post I can't say for sure what the problem is so I will have to list a few things in no particular order. When you say that he can not connect, i interpret that as he can not login on Skype, not that he is logged in but can't make a call.
Step one is that you both need to have individual/separate Skype accounts otherwise you would in effect be trying to call yourself and that is not possible.
Second, if he is able to login to Skype on his iPhone, but the calls do not go through, I would advise trying to complete a call over WiFi first. Starbucks and McDonalds as well as tons of other places have free WiFi. I realize that there are plenty of places around the US where these locations are sparse but just to check that the connection actually works.
He should also check his coverage indicator on the iPhone. Skype video calls usually work great over WiFi, work most of the time on good 3G coverage, but might not work well on E (means EDGE and is basically a slower 2.5G standard that AT&T uses in remote areas.
Good luck and if you post more specifics about what works and what doesn't, we'll be able to help you further.