See the article on the history of bisexual phonelines in the UK for more details, but from its start in 1987 until 1995, when I think it became unviable to repair, the London Bisexual Helpline used a call-diverter box.
Here are the instructions on how to use it that people doing shifts were given…
London Bisexual Helpline
Operation of the call diverter
The call diverter uses two phone numbers:
Line 1 081-569 7500 The helpline
Line 2 081-569 9877 The private line
The public call in on line 1. If the diverter is switched off, the caller will hear a recorded message explaining when the helpline operates, and giving some details of the London groups. If the diverter is switched on, the call is transferred to the volunteer who is on duty.
To switch the diverter on, call the private line (line 2). The phone will ring for about 40 seconds;* when it is answered you will hear a computerised voice saying, "New number please". When this message finishes wait a couple of seconds, then press
16 10 ___**
where ___ is your two-digit location code.
After you have pressed 16, you will hear the message, "Divert off." After you have entered your location code you will hear the message, "Your diversion number is xxx. Divert On." Here xxx is your home phone number.*** Wait for this message to finish before hanging up.
Having set up the diverter, please do not try calling 081-569 7500 yourself to check if the diverter is working correctly. If it is, this will lock up the system!**** Get another phoneliner or a friend to call instead.
To switch the diverter off, call the private line again. This time you will hear the message, "Please hold, your call is being connected" Wait a few seconds and then press 16. You will hear the message, "Divert off."
When you receive a diverted call there is a delay of about four seconds between your phone ringing and the caller being connected. If you pick up the receiver during these four seconds, you will hear a faint click when the call is actually connected.
The call diversion system often results in a poor quality line, so it is a good idea to speak loudly.
These instructions assume you have a tone phone (i.e. a phone which 'bleeps' rather than clicks as you dial). If you don't have a tone phone, you will need a tone pad in order to operate the diverter. The helpline administrator can get you a tone pad if required.
If you have problems switching the diverter on or off, it's possible that you are pressing the digits too quickly, or that you are starting to dial too soon after one of the recorded messages. Any helpliner can switch the diverter on or off for anyone else, so if you cannot get the diverter to work, someone else may be able to help. The call diverter is in Ian Saxton's home; if no one else can help, phone him on 081-568 xxxx.
* It was this long in order to discourage people who called it by accident or otherwise – most of them would have given up waiting long before the end of 40 seconds.
** Looking at them now, clearly the '16' 'divert off' code wasn't actually necessary for the helpline's usage, when the diversion would already be off at the start of a shift. But for other users who'd bought one and who wanted to switch from diverting to number A rather than to number B, it would have been necessary and so would have been in the box's instructions.. to be faithfully copied here.
*** So clearly '10 nn' was the code to say 'divert to the number that's nn-th in the saved list of numbers, but how long that list was (looking at a list of volunteers and the codes for their home phones, it's at least 18) and which of the 11..15 codes you used to set up that list and what the other codes did – delete one of the numbers? read them out for checking? – I never knew.
**** I'd have thought you just got a busy tone, but I never dared try it!