/etc/asterisk/zapata.conf

[trunkgroups]

trunkgroup=>1,24
spanmap => 1,1,0
spanmap => 2,1,1
spanmap => 3,1,2
spanmap => 4,1,3

[channels]

switchtype=national
signalling=pri_cpe
pridialplan=unknown
prilocaldialplan=unknown
usecallerid=yes
callerid=asreceived
echocancel=yes
echocancelwhenbridged=yes
echotraining=yes
rxgain=0.0
txgain=0.0
musiconhold=native
language=en
context=Inbound

group = 1
channel => 1-23,25-72,73-95

/etc/zaptel.conf

span=1,0,0,esf,b8zs
span=2,0,0,esf,b8zs
span=3,0,0,esf,b8zs
span=4,0,0,esf,b8zs

bchan=1-23,25-95
dchan=24,96
loadzone = us
defaultzone = us

From /etc/asterisk/extensions.conf

[GBX-Outbound-Blah]
exten => _1XXXXXXXXXX,1,Set(CDR(accountcode)=${Blah})
exten => _1XXXXXXXXXX,n,Set(CALLERID(all)=Blah <800xxxxxxx>)
exten => _1XXXXXXXXXX,n,Dial(Zap/g1/${EXTEN})

from CLI>
slc-xo-ld-01*CLI> dial 1801xxxxxxx@GBX-Outbound-Blah
[Aug  6 15:49:54] WARNING[7365]: chan_oss.c:682 setformat: Unable to re-open DSP device /dev/dsp: No such file or directory
    -- Executing [1801xxxxxxx@inside:1] Set("OSS/dsp", "CDR(accountcode)=") in new stack
    -- Executing [1801xxxxxxx@inside:2] Set("OSS/dsp", "CALLERID(all)=Blah <800xxxxxxx>") in new stack
    -- Executing [1801xxxxxxx@inside:3] Dial("OSS/dsp", "Zap/g1/1801xxxxxxx") in new stack
[Aug  6 15:49:54] WARNING[7366]: app_dial.c:1099 dial_exec_full: Unable to create channel of type 'Zap' (cause 34 - Circuit/channel congestion)
  == Everyone is busy/congested at this time (1:0/1/0)
  == Auto fallthrough, channel 'OSS/dsp' status is 'CONGESTION'
slc-xo-ld-01*CLI>