Missing design for USSD
Some networks in some countries, especially on pre-paid plans, rely strongly on a feature called Unstructured Supplementary Service Data (USSD) for basic management, which basically are short codes that you enter with dialpad ("Calls" app in this repo), press "dial" and get a message box or menu prompt in return.
Some of the USSD modes are interactive, therefore they need some design mockups, but I couldn't find them in this repository.