you need to set the outbound lines in a hunt so that when one is busy it rolls to the next available.
I have one for a company that has been solid for years where all lines are in a outbound hunt.
This is mine for Australian POTS lines.
Not sure if much different from above but i generally find having a couple to play with makes it work.
#----------------------------------------------------------------#
SN4114/JO/EUI
R6.6 2014-07-11 H323 SIP FXS FXO
2015-01-22T17:09:04
SN/00A0BA0792A3
Generated configuration file
#----------------------------------------------------------------#
cli version 3.20
clock local default-offset +08:00
webserver port 80 language en
sntp-client server primary 202.173.177.171 port 123 version 4
system hostname Patton_SN4114
system
ic voice 0
low-bitrate-codec g729
profile ppp default
profile call-progress-tone defaultDialtone
play 1 1000 425 -6 450 -6
profile call-progress-tone defaultAlertingtone
play 1 400 425 -13 450 -13
pause 2 2000
profile call-progress-tone defaultBusytone
play 1 375 425 -7
pause 2 375
profile call-progress-tone defaultReleasetone
play 1 375 425 -7
pause 2 375
profile call-progress-tone defaultCongestiontone
play 1 375 425 -7
pause 2 375
profile tone-set default
profile voip default
codec 1 g711alaw64k rx-length 20 tx-length 20
codec 2 g711ulaw64k rx-length 20 tx-length 20
fax transmission 1 relay t38-udp
fax transmission 2 bypass g711alaw64k rx-length 10 tx-length 10
profile pstn default
profile sip default
no autonomous-transitioning
profile aaa default
method 1 local
method 2 none
context ip router
interface IF_IP_LAN
ipaddress 10.20.1.253 255.255.255.0
tcp adjust-mss rx mtu
tcp adjust-mss tx mtu
interface IF_IP_WAN
ipaddress dhcp
tcp adjust-mss rx mtu
tcp adjust-mss tx mtu
context cs switch
digit-collection timeout 4
routing-table called-e164 TO_SIP
route default dest-interface IF_SIP_1
interface sip IF_SIP_1
bind context sip-gateway GW_SIP_1
route call dest-service HUNT_FXO
remote 10.20.1.252 5060
early-connect
early-disconnect
interface fxo IF_FXO_1
route call dest-interface IF_SIP_1
loop-break-duration min 200 max 1000
disconnect-signal loop-break
disconnect-signal busy-tone
ring-number on-caller-id
dial-after timeout 1
mute-dialing
caller-id format bell
interface fxo IF_FXO_2
route call dest-interface IF_SIP_1
loop-break-duration min 200 max 1000
disconnect-signal loop-break
disconnect-signal busy-tone
ring-number on-caller-id
dial-after timeout 1
mute-dialing
interface fxo IF_FXO_3
route call dest-interface IF_SIP_1
loop-break-duration min 200 max 1000
disconnect-signal loop-break
disconnect-signal busy-tone
ring-number on-caller-id
dial-after timeout 1
mute-dialing
interface fxo IF_FXO_4
route call dest-interface IF_SIP_1
loop-break-duration min 200 max 1000
disconnect-signal loop-break
disconnect-signal busy-tone
ring-number on-caller-id
dial-after timeout 1
mute-dialing
service hunt-group HUNT_FXO
timeout 4
allows-push-back
drop-cause normal-unspecified
drop-cause no-circuit-channel-available
drop-cause network-out-of-order
drop-cause temporary-failure
drop-cause switching-equipment-congestion
drop-cause access-info-discarded
drop-cause circuit-channel-not-available
drop-cause resources-unavailable
drop-cause user-busy
route call 1 dest-interface IF_FXO_1
route call 2 dest-interface IF_FXO_2
route call 3 dest-interface IF_FXO_3
route call 4 dest-interface IF_FXO_4
context cs switch
no shutdown
context sip-gateway GW_SIP_1
interface LAN
bind interface IF_IP_LAN context router port 5060
context sip-gateway GW_SIP_1
no shutdown
port ethernet 0 0
medium auto
encapsulation ip
bind interface IF_IP_LAN router
no shutdown
port fxo 0 0
use profile fxo au
encapsulation cc-fxo
bind interface IF_FXO_1 switch
no shutdown
port fxo 0 1
use profile fxo au
encapsulation cc-fxo
bind interface IF_FXO_2 switch
no shutdown
port fxo 0 2
use profile fxo au
encapsulation cc-fxo
bind interface IF_FXO_3 switch
no shutdown
port fxo 0 3
use profile fxo au
encapsulation cc-fxo
bind interface IF_FXO_4 switch
no shutdown