Код:
12:39:56 [2297118] 0: Fxs Pickup
12:39:56 [2297118] 0: ==4:GetDtmf
12:40:02 [2297176] 0: DTMF Timeout #1
12:40:02 [2297176] 0: End Input Default Route [0]
12:40:02 [2297176] 0: Line DialNum_New [743662]
12:40:02 [2297176] 0: Call Proxy with [743662]
12:40:02 [2297176] 0: ==7:Inviting
12:40:02 [2297176] 0: VoIP CallOut, Invite <sip:743662@192.168.0.16;user=phone>
12:40:02 [2297177] 0: 701=DIALING
12:40:02 [2297179] 0: 701=PROCEEDING
12:40:02 [2297180] 3: =OFFERING
12:40:02 [2297180] 3: Get CallerId=701
12:40:02 [2297180] 3: Hunting Trunk Line
12:40:02 [2297180] 1: Peer=192.168.0.16#10164, PT=8, RecvOnly=0
12:40:02 [2297180] 1: TrunkPrefix=, Dest=743662, Dialno=743662
12:40:02 [2297180] 1: FxoHookOff
12:40:02 [2297180] 1: InputGain(0)
12:40:02 [2297180] 1: ==18:TrunkDialOut
12:40:03 [2297191] 1: DialOut(743662)=0
12:40:05 [2297204] 1: Fxo DialOut OK
12:40:05 [2297204] 3: =ACCEPT
12:40:05 [2297204] 1: ==13:VoipAnswering
12:40:05 [2297205] 3: =CONNECTED
12:40:05 [2297205] 1: RTP[1,1], Peer=192.168.0.16#10164, PT=8/2/1
12:40:05 [2297205] 1: ==14:Talking
12:40:05 [2297206] 0: 701=CONNECTED
12:40:05 [2297206] 0: Peer=192.168.0.16#14026, PT=8, RecvOnly=0
12:40:05 [2297206] 0: RTP[1,1], Peer=192.168.0.16#14026, PT=8/2/1
12:40:05 [2297206] 0: ==14:Talking
12:40:27 [2297422] 1: Fxo Detected BTC(9)
12:40:27 [2297422] 1: RTP S=1087 R=1079 Lost=0
12:40:27 [2297422] 1: FxoHookOn
12:40:27 [2297422] 1: FxoHookOn
12:40:27 [2297422] 1: Bye at Talking
12:40:27 [2297423] 1: ==15:PlayBusyTone
12:40:27 [2297423] 1: FxoHookOn
12:40:27 [2297423] 1: ==3:Idle
12:40:27 [2297423] 1: InputGain(6)
12:40:27 [2297423] 1: SetFax(1)=0
12:40:27 [2297424] 1: SetModem(0)=-1
12:40:27 [2297424] 3: =DISCONNECT
12:40:27 [2297424] 3: Release Old Dlg #1
12:40:27 [2297425] 0: 701=DISCONNECT
12:40:27 [2297425] 0: RTP S=1093 R=1083 Lost=0
12:40:27 [2297425] 0: Release Active Dlg
12:40:27 [2297425] 0: ==15:PlayBusyTone
12:40:34 [2297496] 0: Fxs Hangup
12:40:34 [2297496] 0: ==3:Idle
12:40:34 [2297496] 0: SetFax(1)=0
12:40:34 [2297496] 0: SetModem(0)=-1
настройки BTC:

Busy Tone мерял лично на собственной линии:
350ms/350ms/426Гц