Panasonic configurations for voicemail with specific pbx:
Panasonic 1232
Panasonic TD500

1- PSTN provides the E1/PRI (EuroISDN)
2- Asterisk receives the PRI
3- Asterisk provides a second PRI to Panasonic
4- Panasonic receives the asterisk PRI

People can receive and make calls on the Panasonic extensions using the
Asterisk public PRI.

PROBLEM: The panasonic users still can’t use the REDIAL button on their
phones, or send faxes, and sometimes we loose some digits that Panasonic sends to Asterisk.

Follow is the relevant config section of the files:

>>> ZAPTEL.CONF

span=1,0,0,ccs,hdb3,crc4
span=2,0,0,ccs,hdb3,crc4

bchan=1-15
dchan=16
bchan=17-31

bchan=32-46
dchan=47
bchan=48-62

>>> ZAPATA.CONF

context=pri-public
switchtype=euroisdn
pridialplan=local
usecallerid=yes
hidecallerid=no
callwaiting=yes
usecallingpres=yes
callwaitingcallerid=yes
threewaycalling=yes
transfer=yes
cancallforward=yes
callreturn=yes
group=1
callgroup=1
pickupgroup=1
immediate=yes
musiconhold=default
signalling = pri_cpe
channel => 1-15
channel => 17-31

context=pri-panasonic
immediate=yes
group=2
overlapdial=yes
signalling = pri_net
channel => 32-46
channel => 48-62

Note: The public PRI is signalled PRI_CPE and the one offered to
Panasonic is signalled PRI_NET

>>> EXTENSIONS.CONF

;
; Context PRI-Public
;
[pri-public]
;
include => default
;
exten => s,1,Answer                    ; Answer the line
exten => s,2,Dial(Zap/g2/2888)    ; Dial to Panasonic and sends the 4
DID digits needed for Panasonic
exten => s,3,Hangup
;
; Context PRI-Panasonic
;
[pri-panasonic]
;
include => default
;
exten => s,1,Answer                          ; Answer the line
exten => s,2,DigitTimeout,2                ; Set Digit Timeout to 5 seconds
exten => s,3,ResponseTimeout,2        ; Set Response Timeout to 10 seconds

exten => _X.,1,Dial(Zap/g1/${EXTEN})
exten => _X.,2,Congestion