WhoCalls will use your modem to detect the CallerID of a calling party. Caller ID (caller identification or CID, and more properly calling number identification CNID, also known as CLID=calling line identity or CLIP=calling line identification presentation) is a telephone service that transmits the caller's number to the called party's telephone equipment during the ringing signal or when the call is being set up but before the call is answered. WhoCalls will not answer the call, just display the caller information (if transmitted). If the caller is already in the database, its details and a photo will be displayed.  
You may also use WhoCalls to display the caller information in an external database. Samples of a Call Center in MsAccess, Excel and MsOutlook are included.
When configured as a server, WhoCalls only needs one modem for the Caller ID detection and then distributes the caller information to its clients on the network.