How to change incoming CallerID

The following is an example of how to add a digit to incoming
CallerID on a particular trunk - some people seem to want this because
their phones will not do a proper callback if the leading digit(s) are
missing.

Step 1: Go into the trunk for that provider (if not a Zap trunk-see
below for Zap) and under Incoming Settings | USER details you will see
a "context=" line - usually this will be "context=from-trunk". Note
what is there now (if it is something other than "from-trunk") and
change it to "from-trunk-custom", or add "-custom" to the end of
whatever is there now

Step 2: Edit etc/asterisk/extensions_custom.conf (you can use nano,
Midnight Commander's built-in editor, or other plain-text editor of
your choice) and add the following at the bottom of the file:

[from-trunk-custom]
exten => _X.,1,Set(CALLERID(num)=0${CALLERID(num)})
exten => _X.,n,Goto(from-trunk,${EXTEN},1)

Again, change the "from-trunk" in the first and third lines if you
originally had something else in your trunk context. In the SECOND
line, the 0 (following the =) is the digit to be added - if you want to
add something other than 0, you'll have to change that.

Step 3: Restart Asterisk

From CLI: restart now (or, restart when convenient if you don't want to drop calls)

OR, from command line: amportal restart

If you need to make this change for your Zap trunk, the procedure is slightly different:

Step 1: Edit etc/asterisk/zapata.conf (you can use nano, Midnight
Commander's built-in editor, or other plain-text editor of your
choice). You will see a "context=" line - usually this will be
"context=from-zaptel". Note what is there now (if it is something other
than "from-zaptel") and change it to "from-zaptel-custom", or add
"-custom" to the end of whatever is there now.

Now continue with Steps 2 and 3 above, substituting "from-zaptel"
(or whatever you found in the "context=" line in zapata.conf) in place
of "from-trunk" in lines 1 and 3 of Step 2 (i.e., just replace "trunk"
with "zaptel" in those lines).

Note that the variable ${CALLERID(num)} is only available in
Asterisk 1.2 and later. If you need to manipulate it in other ways, see
the section on String Handling Functions on the Asterisk variables
page - for example, to always strip the first digit or character off of
incoming Caller ID, you could probably use ${CALLERID(num):1} (adding
the :1 to return all characters AFTER the character in the first
position - this could also be used to strip a leading "+" if a provider
adds that).

Here's another example, in which digits are both removed and added - in the FreePBX forum,
colinjack wrote, "My SIP provider CallerID comes in the format
+44123456789 but my database uses 0123456789 - so I needed to remove
the '+44' and add a '0' to the callerid to allow it to query the user
database." And he added this to extensions_custom.conf to accomplish
this:

[from-trunk-custom]
exten => _X.,1,Set(CALLERID(num)=0${CALLERID(num):3:12})
exten => _X.,n,Goto(from-trunk,${EXTEN},1)

Then he changed his sip trunk context statement to context=from-trunk-custom

Just in case anyone wonders, you can use the same custom context
(in extensions_custom.conf) for multiple trunks, as long as they
originally had the same "context=" destination. Or, if you need to make
different changes to the Caller ID from different trunks, then just
make multiple custom contexts in extensions-custom.conf, and change the
names slightly (e.g. you could call one from-trunk-add-0-custom and
another from-trunk-strip-2-custom, or whatever - just make sure to use
the same context name in the trunk "context=" line and in the header of
your custom context).

Finally, for those using naftali5's Dialplan Injections module,
you can place these code fragments in a Dialplan Injection instead of
extensions_custom.conf. Simply enter the lines beginning with the "Set"
or "Goto" command, like this:

Set(CALLERID(num)=0${CALLERID(num)})
Goto(from-trunk,${EXTEN},1)

Then note the number of the dialplan injection (it will be printed
in angle brackets next to the injection name in the list of
injections), and in your trunk use context=injection-number where number
is the number of the injection. For example, let's say you named the
injection as "Change Caller ID", and after you created it you saw this
in the right hand column: Change Caller ID <15> - in your trunk, you'd then use context=injection-15