said by Bplayer:A POTS splitter is installed, usually at the demarc point but it could be in your room. One output leg goes to the modem/router and the other the the telephone lines.
There are usually three twisted pairs in the telephone wire, so there are lots of options available for the location of the splitter.
not quite true, the point of a pots splitter is to eliminate any taps inside the home and to provide a direct line to the modem so a pots splitter in the bedroom would not be ok, also most older homes there are 2 pairs in a line
I would suggest to clear the point where the line comes in and clear the area around the modem jack