Converged systems, like VoIP, are on the march
http://boston.internet.com/news/article.php/1457951
http://techupdate.zdnet.com/techupdate/stories/main/0,14179,2877029,00.html
It's easy to tap a phone. Keeping a wiretap secret, now that's the tricky part. That’s where the recording equipment and surveillance teams come in. Learn how government spies and other pros go about listening in.
http://www.howstuffworks.com/wiretapping.htm
Cordless phones have been around for about 20 years, but lately they’re a lot more sophisticated -- it seems like you need a Ph.D. to buy one! Find out how cordless phones work and how to buy the right one.
http://www.howstuffworks.com/cordless-telephone.htm
http://www.jkaudio.com/article_03.htm
you should look at your network before installing an IP PBX. But the news is probably good. If not, here's a make-ready recipe, and some products to help.
http://www.cconvergence.com/article/CTM20030204S0006
pinout of most commonly used telephone connectors
http://www.shout.net/~wildixon/telecom/rj/rj11.html
what are the problems when the loop current is too low or high
http://www.sandman.com/loopcur.html