IP Office is Avaya’s small-to-midsize system, launched around 2000. It effectively replaced the Merlin / Partner line in Avaya’s catalog.
What you hear
IP Office doesn’t ship a song. It looks for a file named HoldMusic.wav (8 kHz, 16-bit, mono PCM). If nobody uploaded one and no external source is plugged in, Avaya’s documentation says it plays a double beep tone: 425 Hz, repeated 0.2/0.2/0.2/3.4 seconds on/off.
The clip above is built to exactly that spec and passed through a simulated phone line. We measured our own output at 425.0 Hz with edges at 0, 0.19, 0.40, 0.59, then 4.0 seconds.
Why so many businesses have it
The beep sounds like the phone system is broken, so plenty of offices have run IP Office for years assuming it was a fault. It’s just the default. Upload a HoldMusic.wav to the system’s primary folder and it goes away.
Dial *341# from an IP Office extension to hear whatever the system hold source is set to.