If you find that launching 4th Dimension causes your system to initiate a dial-up connection to the Internet (i.e. your modem dials out), you can remove the TCP/IP Network Component (NC) from 4D to stop this from happening. Note: the 4D TCP/IP component is separate from those used by your operating system.
Follow the links below for directions on adding or removing 4D NCs:
Removing and re-installing NCs on Windows
Removing and re-installing NCs on Mac OS