I'm working on a PHP app which needs to be able to contact someone in the following ways...

Page (if the user's svc doesn't have a Num@mci.com-type msg sender)
Fax (I could send a postscript document, or in any other format)
Voicemail or Answering Machine messages (how does something detect the beep?)

Does anyone have any idea whatsoever as to how to do any of those? Is there a free unix-compatible program that can do any of those (in any programming language of course) that is open source?

Is there a universal paging protocol that all pagers follow? If so, does anyone know where I can read about it? Same thing with fax.

Voicemail and answering machines: this isn't nearly as important but has anyone successfully made a computer application that can deal with these and play a WAV over the line? Without buying a whole phone server like tech support places do..

The phone charges don't matter, and I have access to a completely clear phone line (well, I will soon).

Does anyone have any idea how to do these things?

Thanks a ton, and every reply is greatly appreciated!!