How to Design a Telematics / M2M Server

Hi friends. I know this is sort of a big question, but please bear with me. I have to design a server that will collect information from various mobile sources (vehicles and non-vehicles) which will use GPRS to communicate. Now I am very good at C#/.NET, but I have never done anything like this. Given that the application should be robust and be able to handle hundreds if not thousands of connections, how to go about it? What are the considerations? General (or specific) architecture? Really would appreciate some pointers in the right direction. Thanks!