A line filter allows you to talk on the phone and use your broadband at the same without interference. With a standard install, you’ll need one on every active jack point in the house – Telco jargon for everywhere you’ve got a phone plugged into the wall. Sky TV also counts if you purchase movies through them.
It's really important you do this as without line filters your broadband speed can be impacted.
You can pick a line filter up from your local electronics store for around 20 bucks or less.