The thing you're looking for is called a "DSL Filter". Here's one: http://www.amazon.com/In-line-DSL-Filter-w-Splitter/dp/B001S4I8AQ/ref=sr_1_2?ie=UTF8&s=electronics&qid=1275359801&sr=8-2
You need to put one of these on every phone in the house.
These filters are only needed if your high-speed Internet is via DSL (instead of cable). To find out if you have DSL, look for your modem/router; something from that device should plug into a phone jack in your wall (instead of into a cable TV jack).
Note that your problem may have nothing to do with DSL filters, and instead be caused by interference between the frequency used by your cordless phone and your wireless Internet. If that is the problem, then to fix it, you need to go into the settings for your wireless router and change it to a different channel (it'll probably be on channel 6, try channel 1 or 11 instead).
You need to put one of these on every phone in the house.
These filters are only needed if your high-speed Internet is via DSL (instead of cable). To find out if you have DSL, look for your modem/router; something from that device should plug into a phone jack in your wall (instead of into a cable TV jack).
Note that your problem may have nothing to do with DSL filters, and instead be caused by interference between the frequency used by your cordless phone and your wireless Internet. If that is the problem, then to fix it, you need to go into the settings for your wireless router and change it to a different channel (it'll probably be on channel 6, try channel 1 or 11 instead).