..the exact setup as it's not clear what is connected to what..Are you using Internet Connecting Sharing so that your son's computer is connected through a USB port to your computer and then your computer is plugged into the phone jack? What is the Hub for? Are both computers plugged into the hub which is then plugged into the phone jack? Or maybe there's something else that I'm not understanding..?

Just a suggestion if you're using Internet Connection Sharing..It's not the greatest networking tool...Is there a reason why your son's computer can't connect directly to a phone jack for it's own internet connection?

If you're using ICS, then the link below might help:

How to Troubleshoot Internet Connection Sharing Problems

More information please.

Grif