STEP-1 Configure your DID with your asterisk?

You can find the instructions here.

Now Edit your sip.conf

Add the code below to your ’sip.conf ‘ file

[didforsale_did] type=peer host=[IP Address of our Server] nat=no canreinvite=no disallow=all allow=ulaw allow=alaw dtmfmode=rfc2833 context=from-didforsale insecure=very qualify=yes

In your extensions.conf

[from-didforsale]

exten => _X.,1,Set(CALLERID(num)=${CALLERID(num):1}) include => from-custom-a2billing

Add the . . . → Read More: How to Configure SIP DID from with your asterisk and A2billing