The recent discussions of tapping modem transmissions reminds me of a scrap of data I saw about Caller ID [the service provided by the phone company that displays the caller's phone number whenever your phone rings]. Supposedly, the phone company transmits the caller's number as a burst of 1200 or 2400 baud ASCII between the first and second rings; if your modem is set up 'just right,' you can capture the number with a PC.
I don't know if this is particularly true but you can purchase modems that recognize caller-id and distinctive ring data. The caller-id information is printed between the RING and CONNECT strings. In particular, I have re-written the UNIX getty program in order to take these strings and put them in an environment variable before calling login. Since the getty actually uses ATA to answer the phone rather than setting S0=1, we have considered building a database of known troublemakers' phone numbers and then have getty let the phone ring away to NO CARRIER when said tarbs call. ZyXEL makes such a modem. Jon