We're looking to build a small app that is mainly a calling app. It will call from the phone list of contacts as well as manually entering phone number. The only differences with normal android caller app is: we want to display the calling cost average per minute for different sim card provider. Pricing will be provided in csv format. UI wireframe will also be provided as a rough guideline. For the design itself we would like to stick to android's material design standard. The difficult part that needs to be taken into consideration is different sim card provider will have different pricing based on area/city where you're calling from. So it might require to get the current location of the user.
Basic wireframe is attached in this project.
And also we need to be able to update the pricing data in case there is changes on the pricing.
We can ignore dual sim card functionality for now. So one single sim card is enough.
We might need to have a welcome screen to confirm the user number in case we cannot get that data programmatically, similar to whatsapp when you open the app for the first time. Regarding location I think you can get it via location service (GPS/Cell).
Since we need to update the pricing on the fly, we might need a basic server where we can just upload the pricing csv and it automatically push to all clients.