Every couple of months someone on an Asterisk listings asks why the message waiting lamp on there analog phone doesn't work with a SIP/IAX ATA or FXS. So here is the reason, and I only know because I've been around longer than most. The lamp in the phone is a neon lamp which draws practically no current but requires 90 volts AC to "strike" it. Now the next question should be .. Why doesn't this voltage ring the phone? Well the actual "ringing" frequency is 30 cycles/sec at 90v whereas the neon is at 120 cycles/sec so you could say that the analog line is frequency mutiplexed (I wouldn't say that but you could) In the analog PBX world this requires an addition power supply and special "station" cards so there is little chance of you finding any ATA out there that will do this. There are ways to modify an existing ATA but they all involve getting electrocuted!
Have a good day Henry L.Coleman CEO *VoIP-PBX* 1-866-415-5355 Toronto Ontario Canada
