There are two configuration files for the Warp's chan_gsm channel driver in Asterisk. They are both found in the /etc/asterisk folder on the WARP appliance. The files are called gsm.conf and gsm_additional.conf.
gsm.conf

The gsm.conf file contains settings that apply to all GSM channels in the system. The default example of this file is as shown below.
The last line in the file includes the other file, gsm_additional.conf., see details on it below.

[general]
;Directory where the sms files are stored.
smsdir=/var/spool/asterisk/smsin

;if you want to periodically check for the homezone
check_homezone=yes

;if you want to skip the '+' prefix, set this to yes
skip_plus=no

;set this to yes to enable debugging via syslog
syslogdebug=no

;set this to yes to enable radio/gsm optimzed dtmf detection mechanism
relaxdtmf=no

;set to yes in order to limit the double digit dtmf send
dtmfbegin=yes

;all port configuration should go to gsm_additional.conf
;which has a sample configuration that is commented out
#include gsm_additional.conf


The available parameters in this file and their meanings are as follows. All options here are grouped under the [general] section.
* smsdir - The smsdir option defines the directory where the sms files are stored. Valid values: any directory path that is valid for a linux system.
* check_homezone - The check_homezone option indicates whether the GSM channel driver should periodically check homezone (also measuring signal strength). From the command line, the command "gsm show status" gives the output that is relevant to this option. Valid values: yes no
* skip_plus - The skip_plus option enables/disables skipping the '+' prefix for a number that comes with one. Valid values: yes no
* syslogdebug - The syslogdebug option enables debugging via syslog. Valid values: yes no
* relaxdtmf - The relaxdtmf option enables/disables radio/gsm optimized DTMF detection mechanism. Valid values: yes no
* dtmfbegin - The dtmfbegin option determines when DTMF clamping should be done on the audio frames. Yes means at the beginning of frame, no means at the end of the frame. Valid values: yes no

gsm_additional.conf
This file contains all of the channel specific information for GSM trunks in the system. This is the file written by the freepbx GUI when GSM trunks are added to the system. A sample of this for a single trunk, as generated by the freepbx GUI, is as follows.

;--------------------------------------------------------------------------------;
; Do NOT edit this file as it is auto-generated by FreePBX. All modifications to ;
; this file must be done via the web gui. There are alternative files to make ;
; custom modifications, details at: http://freepbx.org/configuration_files ;
;--------------------------------------------------------------------------------;
;
[from-gsm-custom-1]
sms_pdu_mode=no
smsc=
resetinterval=0
pin=none
initfile=/etc/asterisk/gsm-init-file
hidecallerid=no
exten=s
context=from-gsm
channel=>1

This file is over written every time configuration is applied in the FreePBX GUI. The available parameters in this file and their meanings are as follows.
* channel - The channel option defines the channel number(s) the configuration will apply to. If there is more than one channel, they are comma separated. Valid values: Comma separated list of channel numbers.
* initfile - The initfile option specifies the file that contains the collection of commands used to initialize the GSM radio. Valid values: A path to an initialization file with the correct format. If this option is left empty, a default initialization sequence will be used.
* context - The context option specifies the context to be used under the dialplan for incoming calls. Valid values: A valid context name
* exten - The exten option specifies the extension to be used for incoming calls. Valid values: A valid extension
* pin - This is the PIN (Personal Identification Number) setting required by the SIM card for authentication. Please set this option to none if your SIM card does not require any PIN entry for operation. If a PIN number is required by the SIM card, please ensure it is set to the correct value for successful authentication.
* hidecallerid - The hidecallerid option specifies whether the caller ID is to be hidden when making outgoing calls. Valid values: yes no
* resetinterval - The resetinterval option defines the number of seconds to elapse after which the channel(s) is to be reset (when not in use). Leave as 0 to disable this option. Valid values: 0..N
* smsc - SMSC is a setting for the Short Message Service Center number, which should normally be already set in your SIM card. If you do not know the SMSC setting or do not need or want to change it, please set this option to none, or leave it blank, so the default setting in your SIM card will be used. Using an incorrect setting here will cause the SMS messaging to fail.
* sms_pdu_mode - The sms_pdu_mode option specifies whether the SMS should be provided in PDU or in cleartext format. Valid values: yes no
* txgain/rxgain - These options increase or decrease the gain applied to the GSM channel