The only poem I've written in more than one voice was part of my 2005 ERRATA chapbook. It was written for a forms class in my MFA and I think the only time I've heard it read aloud was in that class. I've always been to do a whole book like this, but it might be a little much...
This was also one of the pieces that did not travel with much of the chap into my second book, IN THE BIRD MUSEUM, but you can read a pdf of the original project in its entirety here: