Someone

exten => 200,1,Answer()
exten => 200,2,Goto(GSMmain,s,1)

[GSMmain]

exten => s,1,Ringing
exten => s,n,Set(TIMEOUT(digit)=5)      ; Set Digit Timeout to 5 seconds
exten => s,n,Set(TIMEOUT(response)=10)  ; Set Response Timeout to 10 seconds
exten => s,n,Background(demo-thanks)                ; "Thanks for calling press 1 for sales, 2for support, ..."
exten => s,n,WaitExten
exten => 1,1,Goto(GSMsub,s,1)
exten => 2,1,Hangup
exten => 3,1,Dial(SIP/dennis@dennis,15|tT)

[GSMsub]
exten => s,1,Ringing                                   ; Make them comfortable with 2 seconds of ringback
exten => s,n,Wait,5
exten => s,n,Background(queue-periodic-announce)   ; "Thanks for calling the sales department. Press 1 for steve, 2 for..."
exten => s,n,WaitExten
exten => 1,1,Goto(default,206,1)
exten => 2,1,Goto(default,207,2)