I run Bill's fan page on Facebook, and have been in contact with him by phone and mail many times over the last couple years. Between this site and Facebook, he absolutely LOVES hearing from everyone. When I first started the Facebook page, he thought that people had pretty well forgotten about him, so it makes him happy that people are remembering his work.
In regards to anyone who hasn't heard back from him in a timely manner, I should tell you that the talent agency listed no longer represents him. If I remember correctly when this came up in one of our previous calls, I believe he said they forward things to him still, but it can take extra time. Bill graciously gave me permission to post his direct PO Box on the Facebook fan page. I invite everyone to come over and "like" the page, check out all the pics and videos of Bill's work, and jot down his address to drop him a line! He loves hearing from everyone, and he said he's heard from lots of people from around the world since I posted his address. Here's the link:
http://www.facebook.com/billphippsfanpage