Something

[general]
static=yes
writeprotect=no

[globals]
CONSOLE=Console/dsp
OUT-1 = SIP/TSI
TRUNK=[removed]

[dialing]

exten => s,1,Set(TIMEOUT(response)=3)
exten => s,2,Set(TIMEOUT(digit)=15)

exten => t,1,Playtones(busy)

exten => _NXXNXXXXXX,1,Dial($TRUNK/${EXTEN},60)

exten => i,1,Playtones(busy) ; happens for single digits

[default]

exten => s,1,Answer
exten => s,2,NoOp("Incoming call from ${CALLERIDNUM}")
exten => s,3,Playtones(dial)
exten => s,4,Set(TIMEOUT(digit)=3)
exten => s,5,Set(TIMEOUT(response)=15)

exten => 1,1,StopPlayTones
exten => 1,2,Goto(dialing,s,1)

exten => i,1,Playback("invalid")
exten => i,2,Hangup

exten => t,1,Goto(s,3)