There are two cables available. The phone internally has a serial interface and a seperate USB interface. The cables will connect to one of these interfaces. The other end that plugs into your computer is USB. Either cable is available at Radio Shack for $20 and are made by FutureDial.
This cable has a blob half way along the cable that converts from USB to serial and then connects to the serial interface in the phone. The chip inside the cable is a Prolific 2303 and this is how your operating system will report it. It is marked as for the LG VX1/10 but works fine on the VX4400.
Sometimes the phone does not respond when using this cable, and has to be
manually forced to talk. Do this by Menu 
8-Settings 6-Data Settings 2-Select Port
RS-232C(COM Port)
Windows
This cable works well and is reliable. You will need to obtain the drivers from FutureDial.
Linux
Linux has drivers builtin. Note: There is a bug in the Linux 2.4 kernel that causes many machines to crash when any program stops using the cable. This has been fixed in the 2.6 kernel.
Mac
Mac OS X has drivers builtin.
This cable connects to the USB interface inside the phone. The cable is marked as for the LG VX4400 and the LG 5350.
Windows
You will need to install the drivers from FutureDial. Two interfaces are created. One is for using the phone as a modem, and the second is "diagnostic serial port". The latter is what BitPim uses.
Note: There is a driver bug where data will suddenly stop being returned. It happens a lot of the time to a lot of machines. For most people it usually happens while reading the phonebook. There is no known work around. It is recommended that you return the cable to Radio Shack and get the USB to serial one which doesn't have this problem. You may also want to mention this issue to FutureDial support.
Linux, Mac
There are no drivers for these platforms, and you cannot use the cable with them.
BitPim 0.62 06 November 2003