extensions.conf:

[Menu]
exten => s,1,ResponseTimeout,15
exten => s,2,Background(main-menu)
exten => s,3,DigitTimeout,15
exten => s,4,NoOp(After Background)
exten => 1,1,NoOp(Menu-1)
exten => 2,1,NoOp(Menu-2)
exten => i,1,NoOp(Menu-invalid)
exten => t,1,NoOp(Menu-timeout)

[from-sip-internal]
exten => 1,1,Answer
exten => 1,2,Goto,Menu|s|1
exten => i,1,NoOp(sip-invalid)
exten => t,1,NoOp(sip-timeout)


console output:
 -- Executing Answer("SIP/dev1-0660", "") in new stack
    -- Executing Goto("SIP/dev1-0660", "Menu|s|1") in new stack
    -- Goto (Menu,s,1)
    -- Executing ResponseTimeout("SIP/dev1-0660", "15") in new stack
    -- Set Response Timeout to 15
    -- Executing BackGround("SIP/dev1-0660", "main-menu") in new stack
    -- Playing 'main-menu' (language 'en')
    -- Executing DigitTimeout("SIP/dev1-0660", "15") in new stack
    -- Set Digit Timeout to 15
    -- Executing NoOp("SIP/dev1-0660", "After Background") in new stack
  == Auto fallthrough, channel 'SIP/dev1-0660' status is 'UNKNOWN'
    -- Executing NoOp("SIP/dev1-0660", "Menu-hangup") in new stack