Some older AT&T answering machines such as 1715 and 1717 have a feature called "Room Monitor with Intercom" that can be used for paging and half duplex hands free conversations. These machines require you to enter a DTMF code to access the remote control mode, once you have entered this mode you need to enter additional DTMF codes to enter the intercom mode. This can however be automated using the 'D' parameter in the Dial command.

These machines are available on eBay from time to time and are very inexpensive.

The following settings illustrate using AT&T 1717 for paging and intercom

Prepare the answering machine

• Record a 6-7 seconds long outgoing message, the message can be used for announcing that a page is about to commence
• Set the machine to answer on 2 rings
• Set the volume to the appropriate level for your environment
• Make sure that your FXS device can play DTMF tones that are recognised by the machine, I had to change the DTMF settings on both PAP2 and asterisk to inband for DTMF to be recognised properly
• Additionally you can wire an external speaker or amplifier to the speaker wires, but to do this you will need to open the box and take out your soldering iron

Asterisks settings

• Create an extention for the FXS device to which the answering machine will be connected and set the dtmf mode to inband
• Make the following entries in the extensions_custom.conf to dial the answering machine and play DTMF

In the above example *20 dials extention 220 and plays the DTMF codes to enter the paging mode. The remote access code for the machine in this example is 999, after dialing 999 we need wait a few more second before we can we dial 98 to enter the intercom mode. When you first enter the intercom mode, this machine is designed to go in the remote monitoring mode which allows you to listen to the sounds in the room, to broadcast we need to send it another '8'. Each 'w' provides a 0.5 second pause. Notice the 'w' between each number, this machine doesn't recognise DTMF if it is sent too quickly.

During the call you can switch back and forth between listening and speaking by pressing 8 on the handset.


Please note that I only have experience with Trixbox so please adjust the above according to your asterisk installation.

See Also

• Asterisk Paging and Intercom
• AT&T page for answering machines manuals
• Database Systems Corp. - Answer Machine Detection for predictive dialers and autodialers.