Android, Iphone, Blackberry dialer, NOT IP dialer

The need is a dialer for the 3 phone os described in title which could replace the existing one with the capability to dial a gateway number prior to send the number entered by the end user and then terminate the send by a specific string. The gateway number has to be dialed only when the number entered by the end user starts by a specific pattern. This process has to be fully transparent for the end user.