I need add prefix to callerid for all calls in trunk

General Help
1

i have scheme: Conpany1 - SIP trunk - Company2.

i need for calls Company1 to Company2 set callerid = 77+callerid, for calls Company2 to Company1 set callerid = 76+callerid. i need help me.

2

Would be really glad to understand how to do such thing with FreePBX too.

There is a module called “set callerid”. From what I understood, you need to configure :

Description : name
CallerID Name: CustomCID - ${CALLERID(name)}
CallerID Number: 2${CALLERID(num)}
Destination: ???

Once done, I suppose (but not sure) that the only place to add it is either an IVR or an Inbound route.

The destination is not clear too as the aim would be to append CallerID name and/or number for the whole SIP/IAX trunk to all extensions from both sides.

Any example on how to achieve that?
I have fond the user guide (http://literature.schmoozecom.com/set_callerid-module/userguides/set_callerid_module-userguide.pdf ) but this case is not listed.

Thanks,
Alex