sip.conf

[GBX-SIP]
type=friend
canreinvite=no
context=GBX-Inbound
host=x.x.x.x
externip=x.x.x.x
disallow=all
allow=gsm
allow=ulaw
allow=alaw
;qualify=yes
nat=no
account=GBX-SIP

extentions.conf

[GBX-Inbound]
;SIP Test
exten => _XXXXXXXXXX,1,Playback(tt-monkeys)


    -- Executing [XXXXXXXXXX@GBX-Inbound:1] Playback("SIP/5060-09bb7f00", "tt-monkeys") in new stack
    -- <SIP/5060-09bb7f00> Playing 'tt-monkeys' (language 'en')
  == Auto fallthrough, channel 'SIP/5060-09bb7f00' status is 'UNKNOWN'
[Jul 26 04:21:42] WARNING[7744]: chan_sip.c:1900 retrans_pkt: Maximum retries exceeded on transmission SDl69rb01-118656ce89b7b0342946bb859afade11-v3000i1 for seqno 29646 (Critical Response)
localhost*CLI>