from zaptel.conf:

span=1,2,0,ccs,hdb3,crc4
bchan=1-15
dchan=16
bchan=17-31

from zapata.conf:
context=from-zaptel-port1
group=1
signalling=pri_cpe
channel => 1-15,17-31

when i dial:
    -- Called G1/XXX
  == Primary D-Channel on span 1 down
May 24 15:57:40 WARNING[10870]: chan_zap.c:2445 pri_find_dchan: No D-channels available!  Using Primary channel 16 as D-channel anyway!
    -- Hungup 'Zap/31-1'
  == Everyone is busy/congested at this time (1:0/0/1)
    -- Executing Hangup("SIP/113-08282fe0", "") in new stack
  == Spawn extension (dial-mobile, h, 1) exited non-zero on 'SIP/113-08282fe0'
  == Primary D-Channel on span 1 down
May 24 15:57:43 WARNING[10870]: chan_zap.c:2445 pri_find_dchan: No D-channels available!  Using Primary channel 16 as D-channel anyway!