Paul,
Normally, at least if you're calling a fixed line you'll just get a ringing tone once you dial the last digit but the routing tone does appear now and again.
It was much more common when there were still a few crossbars on the local network. The "parent" Alcatel E10 would produce it for a few seconds while the older exchange was doing the final local switching stages.
You'll still hear it before a mobile phone rings (on some exchanges). It also pops up if you call a number that lets calls queue until a hunt group line is free e.g. some operator services that don't have "please hold" announcements in place.
Also international calls to countries that either have old networks or where connection isn't instantanious.
basically anytime there might be a silence before the ring tone/engaged tone/announcement.
Although I've noticed a couple of "bebebe"s when calling normal land lines from some remote rural spots. Not sure why.. there are no non-digital switches and signalling is all SS7.. maybe just an early E10 with slow processing.
The older (long gone) Ericsson ARF crossbars used to make a soft very regular "tick tick tick" noise while they were switching. I don't think it was just the noise generated by the switching process it was actually a specifically generated "tone". Sounded like a clock ticking followed by a clunk (generated by the switching process) before ringing.
Strangely enough ARFs usually accepted tone dialling but would return the "wrong number tritone" if you dialled * or # or just ignore it completely. The number didn't seem to be translated to pulses either, at least not that you could hear. I think they were quite possibily, like in Australia, retrofitted with computer controls and some electronic registers etc. i.e. kinda hybrid crossbars. I know they could provide call diversion and call waiting.
I'd say that the partial computerisation was prob. so they could handle non-unit based billing and detailed statements etc. I doubt provision of tone dialling was a huge priority.
[This message has been edited by djk (edited 05-09-2003).]
