Can anyone provide a bit more info on how this setting works?
I think it functions by plugging a value in - for example 2 - and after you have two channels in use for a particular extension, it returns a busy if a third call tries to come into that extension, but I’m not 100% sure.
By default in FreePBX (device_state_busy_at=0) when you’re talking on your extension regardless of how many channels are open to your phone, the device state reports as “InUse”. When you hang up it goes back to “Idle”. If you set the device_state_busy_at value above 0, then the device state will change from “InUse” to “Busy” when you hit the channel threshold.
You can test this from the asterisk console.
Phone is in use with default setting:
CLI> core show hint 6008
6008@ext-local : PJSIP/986008&PJSIP/9 State:InUse Presence:available Watchers 2
Phone in use with device_state_busy_at value to 1
CLI> core show hint 6008
6008@ext-local : PJSIP/986008&PJSIP/9 State:Busy Presence:available Watchers 2
Unless you’re writing some custom dialplan, I can’t think of anywhere in the dialplan that it will make much of a difference in FreePBX.