Ringing before forwarding


I have the following requirement from my installation of freepbx: sip peer dials internal number and I should forward it to mobile number. I have implemented it by adding extension 123, forwarded all incoming calls to the a mobile number and told the peer to call this extension. Forwarding works fine, but I have the following issue: when somebody got forwarded to the mobile number freepbx answers before the actual forwarding and the person hears free signal when the outside trunk makes progress to the actuall call - it is misleading and annoys our customers big deal. Strange enough, when I call from inside its ok. I tried numerous suggestions and solutions, but to no avail. Could you please advise me how to mend the situation?