extension.conf:

exten => fax,1,SetVar(FAXFILE=/var/spool/asterisk/fax/${CALLERIDNUM}.tif)
exten => fax,n,SetVar(FAXFILENOEXT=/var/spool/asterisk/fax/${CALLERIDNUM})
exten => fax,n,rxfax(${FAXFILE})
exten => fax,n,System('/usr/bin/fax2mail ${CALLERIDNUM} "${CALLERIDNAME}" 01524832280 MattFletcher matt@pinkdylan.co.uk ${FAXFILENOEXT} n')

################################################################################################

zapata.conf:

[trunkgroups]

; define any trunk groups

[channels]

; hardware channels

; default

hidecallerid=no
usecallerid=yes
ukcallerid=yes
cidsignalling=v23 ; Added for UK CLI detection
cidstart=polarity ; Added for UK CLI detection
callwaiting=no
threewaycalling=yes
transfer=yes
echocancel=yes
echotraining=yes
faxdetect=incoming
;txgain=9
;rxgain=9

; define channels

signalling=fxo_ks
callerid="Emma" <400>
sendcalleridafter=2
mailbox=400
context=outbound-emma
channel => 1

context=inbound-emma ; Incoming calls go to [inbound-emma] in extensions.conf
signalling=fxs_ks ; Use FXS signalling for an FXO channel
callerid=asreceived ; propagate the CID received from BT
channel => 2 ; PSTNs attached to ports 2-4

context=inbound ; Incoming calls go to [inbound] in extensions.conf
signalling=fxs_ks ; Use FXS signalling for an FXO channel
callerid=asreceived ; propagate the CID received from BT
group = 1
channel => 3-4 ; PSTNs attached to ports 3 & 4

################################################################################################

Asterisk Console Output:

  == Starting post polarity CID detection on channel 4
    -- Starting simple switch on 'Zap/4-1'
    -- Executing Verbose("Zap/4-1", "Incoming call from BT line - CallerID=01524416379") in new stack
Incoming call from BT line - CallerID=01524416379
    -- Executing Answer("Zap/4-1", "") in new stack
    -- Executing SetMusicOnHold("Zap/4-1", "default") in new stack
    -- Executing BackGround("Zap/4-1", "pd-menu-main") in new stack
    -- Playing 'pd-menu-main' (language 'en')
asterisk1*CLI>
Disconnected from Asterisk server
Executing last minute cleanups

################################################################################################

/var/log/messages:

Nov  8 06:25:05 asterisk1 exiting on signal 15
Nov  8 06:25:06 asterisk1 syslogd 1.4.1#17ubuntu7: restart.