Android/Iphone SIP Dialer with Call back functionality

We are looking for to outsource a project for multiplatform SIP dialer for mobile devices. It should support features like G729 codec support, tunneling, high quality voice, call back feature (it is customized feature where a web request would be required to be initated). Dialer should be able to display balance from VOIPswitch but will not use call back feature of the VOIPswitch. It should be fully customiazable with our logo and brands and customized registration process. Please contact us if you ALREADY have experience of such a project. No experiments please