Asterisk: easily forward Sipgate-calls while keeping the caller-id

This article describes how to forward phone calls that are incoming on a Sipgate VoIP-based number to any given mobile or landline in an affordable way by using FreeVoipDeal. Prerequisites are accounts at Sipgate, FreeVoipDeal and of course your own PBX based on Asterisk.

Configuring an Asterisk PBX is rocket science in itself. To keep this article focused on the main issue I therefore assume you already have a running setup.

In order to forward calls you'll have to use the Windows client of FreeVoipDeal. There you can configure a general forward number which can be a landline or mobile number. Also, you'll have to allow access to the SIP-server of FreeVoipDeal - that is deactivated by default. Now you can use you FreeVoipDeal-account to receive incoming SIP-based calls on

The tricky part is how to keep the caller's number intact while forwarding. In your extensions.conf you'll therefore have to add the following lines:

exten => s,1,Set(CALLERID(name)=${IF($[${CALLERID(number)} = anonymous] ?  anonymous : 49${CALLERID(number):1} )})
exten => s,n,Set(CALLERID(number)=${IF($[${CALLERID(number)} = anonymous] ?  anonymous : 49${CALLERID(number):1} )})
exten => s,n,Dial(SIP/,,tkw)

Now all your incoming calls are going to be forwarded to your designated number.

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