Softphone software for IOS and Android

We would like to develop a softphone client similar to 3CX Phone but with a different approach included. There are some open source softphone that could be used as base. The softphone will need our brand on it and besides operate as any regular softphone an additional feature is expected: There will be a configuration that allows a different way of making call. If some parameter is defined, instead of have a SIP extension registered on softphone, it will send the number dialed to Asterisk server with the mobile number (person that is dialing) to Asterisk Server, then Asterisk will call for both numbers (destination number and dialer number). The final result of this project will be: a) Softphone for Android and IOS devices b) Asterisk scripts or configuration to accomplished the above scenario. Feel free to contact me to gather additional information about the project.