Programme for mobíle phones to enable it to use callthrough automatically

we need a programme, that allows the user of a mobile phone that this device uses a certain prefix depending on the target taht should be a´called (least cost routing). To ensure that the mobile operator cannot bar the number dialed, this number shall be changed after each connection. So the mobile must store a new call through number at the end of each connection. This number can be obtained automatically through the network by sending it when terminating the call or it can bei transmitted when the call is still running. The programme shall run on every inportant software platform for handies in Europe (Symbias OS as well as others).