This is what comes across the console when the call is being placed.  Notice how Asterisk is trying to route the call to it's incoming calls context in extensions.conf 


  -- Executing [12392449062@jamko_phones:1] Set("SIP/mediatrix1-0000006f", "SPYGROUP=10005") in new stack
    -- Executing [12392449062@jamko_phones:2] Dial("SIP/mediatrix1-0000006f", "SIP/12392449062@my_service_provider_4,120") in new stack
  == Using SIP RTP CoS mark 5
  == Using UDPTL CoS mark 5
    -- Called 12392449062@my_service_provider_4
    -- SIP/my_service_provider_4-00000070 is making progress passing it to SIP/mediatrix1-0000006f
    -- Now forwarding SIP/mediatrix1-0000006f to 'Local/2396346540@incoming_calls' (thanks to SIP/my_service_provider_4-00000070)
[Aug 11 13:34:27] NOTICE[30752]: chan_local.c:534 local_call: No such extension/context 2396346540@incoming_calls while calling Local channel
[Aug 11 13:34:27] NOTICE[30752]: app_dial.c:789 do_forward: Failed to dial on local channel for call forward to '2396346540@incoming_calls'
  == Everyone is busy/congested at this time (1:0/0/1)
    -- Auto fallthrough, channel 'SIP/mediatrix1-0000006f' status is 'CHANUNAVAIL'