Customer mapping with GPS Integration

We need an iPhone app (and maybe an Android version as well) that will take a customer list and display it as markers on a map. In addition the user's current position should be fixed by GPS, so that the map is centered on the user's position thereby displaying the customers closest to the users position. The customer information, such as full address, telephone, contact names and email will be available by clicking on the marker. I don't think point-to-point directions will be required, as the purpose of the app is to allow our people to call on people they are in close proximity to. It needs to be possible for each salesperson to load, modify and delete their customer data into the app, by importing some sort of standardized file - comma-delimited text or what have you. The app would be branded with our corporate logo, which I can provide the required format.