creating modem pool in a server

Hi,

how to create a modem pool in a server. which can handle multiple calls come from n number of client to a server. A server contains 5 to 10 modems to handle these calls but sometime suppose one modem busy so with modem pool technology automatically switch over the other modem if a modems gets busy.

how to achieve this type of architecture.
plz help me out i m unaware of this type technology. its urgent.