Wow. You asked for my advice on how to handle this, but I'm having a lot of conflicting thoughts.
On one hand, I have some real compassion for the other husband. I understand the driving need for him to want to keep tabs on what is going on with his W. I'm one of the few on this board who advocates snooping. My motto was "trust, but verify" although I know that for some it becomes near obsession. I found that I needed to check every so often to make sure actions were matching words. It did, so I eventually got to the point where it doesn't occur to me to snoop but every once in awhile. I've heard of quite a few cases where the betrayed spouses kept in contact for awhile to compare notes.
On the other hand, his contacting your H, and his W contacting your H feels just, well icky. You're right, it does seem to be creating a self-perpetuating situation with continuing the contact.
On the THIRD hand (LOL!) having to deal with the continuing drama seems to be wearing on your H's patience. It sounds like he's getting quite sick of it. And there you are, being the attractive alternative--which is a good place for you to be!
This is what I'd do. The next time your H complains about this, ask him if he's ready to change the phone numbers and follow that up with NO face to face contact either. They don't need YOU, they need a MC! It needs to really be HIS decision and he should be ready to do it with conviction.
