We've had several discussions relating to telephones in the the past, so as it's quiet in here at the moment I thought I'd revive this topic.
I finally had a little spare time a few days ago, so I rigged up a phone patch and put together a short demonstration of what the modern British system sounds like, from basic calls through to the engineering test systems.
It's an MP3 recording, so if anyone wants to hear it, let me know on this thread or drop me an e-mail and I'll forward it to you.
WARNING: The file is approx. 13.6MB, so allow plenty of download time. (OK for you broadband guys.....