OK, another super simple script anyone can write that should be included with Thirdlane PBX because it's handy. Voip-info says this is a 1000Hz tone. A milliwatt is officially 1004Hz. My analog meter says it's 1004Hz. In either case it's a handy test to have available. I have it ring for a moment so if I'm not measuring it with a meter and using a phone I have a moment to know it's connecting and get it away from my ear before it blows me away.
Add it to your list if you find it useful.
; silly little useful script
; answers and plays a 0db 1004 Hz tone
exten => s,1,answer
exten => s,n,ringing
exten => s,n,Wait(3)
exten => s,n,Milliwatt()