Hello where can I install my sim card in the controller and is it possible to work with the developer sdk to install custom made applications.

You cannot install any simcard in the RC. There are some rumors that DJI will provide an external module some day.
Currently there is no possibility to install any kind of third party apps.

Hi there. Thank you for reaching out. Kindly please refer to the statement of MySky on post #2. We will also take this as suggestion of yours and will forward to our designated team for attention. Thank you for your valued support.