I assume you mean a fully functional GSM/GPRS modem when you talk about “Wavecom module” (a module is only a component that needs alot of peripheral circuits to work as a modem)
If you have a GSM/GPRS modem with serial V24 interface then you could connect it to the PC serial port (COM1 or something).
Then you write a PC application that can control the modem to connect, either in circuitswitched GSM mode or in packed switched GPRS mode, to an ISP. Then you will have an wireless Internet access over the PC-modem.
The next application (you also need to write) is the one that runs inside the remote stand-alone modems. This application basically has to do the same thing as the PC application before the different units can send data to each other.
The different ways to connect (from the PC and from the modem application) are many and include decisions about programming environment on the PC side, communication interfaces, network subscriptions etc…
Your question is very general so I don’t think I can post a more detailed reply for now.