I have some home audio equipment with network jacks. Most phone line jacks I've seen tend to be 4 or 6 connector. In the home, they are generally 4 connector which allow service for 2 lines. Network jacks (RJ45) are similar to phone jacks but have 8 connectors. In other computer systems, these tend to be proprietary connections for special features available for specific devices that allow them to be connected to other devices or even PCs if the right software is installed. I doubt they are for firmware updates.
A brief definition of "firmware" might be software that is built into hardware. Firmware chips contain specific instructions used in the operation of the device. Examples of devices that have firmware installed are digital cameras, scanners, some printers, portable devices such as PDAs, etc. Hard drives and CD/DVD burners also have firmware. These are sometimes upgradable as new features are added or bugs are found. The manufacturer will release what might be called a "ROM" file which can replace the software imbedded in the firmware chip. Accessing the chip will require special software as well and the manufacturer will provide this if it's meant for public release. Basically, you run the software which erases the old firmware code and replaces it with new code. You do this very carefully as it's possible to corrupt a device and make it unusable. It's advisable to read about the new code before installing it as it may contain a list of features or fixes contained within it. If the new code corrects problems you are not likely to have, such as those specific to a language or device connection which you do not own, there is no use in risking an update. Hope this helps.
Besides computer hardware I also notice phone line connections for other home or car entertainment equipment, such as a phoneline connection on a car amplifier, I wonder if that is for firmware also?
I have never done a firmware update. How essential is it for the operation of your system to do these types of updates? I appreciate the knowledge in cnet forums, so knowledge is never forsaken.