Code:

exten => _8.,1,GotoIf($[${EXTEN:1:3} = 416]?2:10)
exten => _8.,2,GotoIf($[${EXTEN:1:3} = 905]?3:10)
exten => _8.,3,SayDigits(${EXTEN})
exten => _8.,4,Hangup
exten => _8.,10,Set(NEWEXT=1${EXTEN:1})
exten => _8.,11,SayDigits(${NEWEXT})
exten => _8.,12,Hangup

CLI:

   -- Executing GotoIf("SIP/204-081c05e0", "0?2:10") in new stack
    -- Goto (out.auricnet,855239,10)
    -- Executing Set("SIP/204-081c05e0", "NEWEXT=155239") in new stack
    -- Executing SayDigits("SIP/204-081c05e0", "155239") in new stack
    -- Playing 'digits/1' (language 'en')
    -- Playing 'digits/5' (language 'en')
    -- Playing 'digits/5' (language 'en')
    -- Playing 'digits/2' (language 'en')
    -- Playing 'digits/3' (language 'en')
    -- Playing 'digits/9' (language 'en')
    -- Executing Hangup("SIP/204-081c05e0", "") in new stack
  == Spawn extension (out.auricnet, 855239, 12) exited non-zero on 'SIP/204-081c05e0'
    -- Executing GotoIf("SIP/204-081f24c8", "0?2:10") in new stack
    -- Goto (out.auricnet,841655,10)
    -- Executing Set("SIP/204-081f24c8", "NEWEXT=141655") in new stack
    -- Executing SayDigits("SIP/204-081f24c8", "141655") in new stack
    -- Playing 'digits/1' (language 'en')
    -- Playing 'digits/4' (language 'en')
    -- Playing 'digits/1' (language 'en')
    -- Playing 'digits/6' (language 'en')
    -- Playing 'digits/5' (language 'en')
    -- Executing Hangup("SIP/204-081c05e0", "") in new stack
  == Spawn extension (out.auricnet, 841655, 11) exited non-zero on 'SIP/204-081f24c8'

    -- Executing NoOp("SIP/204-081badb0", "Extension 416") in new stack
    -- Executing NoOp("SIP/204-081badb0", "Extension 165") in new stack