I'm blegging you!

If you haven't seen the term before, "bleg" is blog-speak for "beg," i.e. to ask for assistance. Well, I need some assistance (in more ways than one!)...

Can anybody point me to a good source for the history of calling priests "Father"? Note: I am not asking for justification for the practice... I do it all the time, and I know why, on what basis, and how it doesn't violate Matthew 23:9.

What I'm interested is the actual historical development of the practice. When did priests begin to be addressed in this manner? Anybody know?