Servers

Friends: I have a customer that wants to connect several remote machines through phone access (with a card DIGI, or similar) with a central server that administers several servers in turn. The remote clients send petitions to the server, and this central server would have to authenticate the access, to receive the petition, to guide (routing) it to the corresponding server, to receive the answer and to return it to the remote client. Can I make that with Linux? Of to be this way, Which the approximate steps would be to achieve this task? thank you Ernesto