I don't understand the question completely. Do you want to develop a mobile website or a general website? First of all, I think banks won't allow third party developers to talk to their servers as this will be a potential security issue. I don't know about banks in Zimbabwe. If somebody from the bank approached you to build an app then that is fine. If you are planning for a mobile application, then you need to find which devices are mostly used in your country and build an application for that. For example,
1) If Nokia S40 devices are more then you need to go with Java applications
2) If Android is used more then you need to download the Android SDK, build the app and publish to the app store.