If you email me a pitch, include your phone number in the message.
If you don’t want to put a phone number on your email, put it on your Web site.
If you don’t put a phone number on your Web site or your email, I guess you don’t want to talk to the press.
If you don’t want to talk to the press, what are you doing in the PR business?
Your call is very unimportant to us.
See also: Tip #2, Followup immediately
Rafe
Pro PR Tips 
I’ve noticed this kind of things, and never really understood that. It’s like you said, if you don’t want to talk to the press, why working as a PR person? Find some other job where no one will bother you…