Custom Call Forwarding App for Andriod

I want to have a call forwarding application created for my andriod phone. The call forwarding application should be able to transfer all incoming calls to an international number. The idea I have for the application is as follows: 1. My phone will have the GSM SIM in it. When I start the call forwarding application, it should ask me the number that all incoming calls need to be forwarded to. 2. Now when any call comes, it should receive that call and play a default dial tone or sound. 3. In the backend, it should initiate a new call using the GSM SIM in phone and dial the number the that was entered in the app. 4. As so as the number is answered, it should merge both the calls, hence connecting the caller and the entered number in a conference call. The default call forwarding apps rely on the call forwarding capability of the GSM provider and do not fulfill my requirement. If anybody has other ideas then they are welcome as well. My main requirement is that any call coming on my local SIM, should be received irrespective of the country I am in.