Ever since I've read past the CCNA:Voice section regarding Music on Hold (MOH) I've been trying to get it working ever since. The problem I ran into is that I couldn't get MOH to work when I placed a call from one IP Phone to another in my internal network, just dead silence. After some research, apparently this a known issue depending on how you configure MOH. In order for this to work between IP Phones in your internal network, you're supposed to use multicast rather than the default method. Even with multicast configured and every option I could think of, I still couldn't get this working.
Well after completely forgetting about MOH and eventually setting up my remote network weeks later, I was reviewing a few CBT's when it hit me that MOH should work when putting external callers on hold. I placed a call to the analog phone on the remote network and then put them on hold, sure enough it worked! I will admit though that the quality wasn't great because I was using the G.729 codec across my WAN and I'm betting that this analog phone is at least 15 years old!