Aztech DSL Phone Splitter is designed with 2 RJ11 Tel Jacks for high high speed ADSL data transfer and regular voice call for telephone or fax.. The POTS DSL Phone Splitter works by blocking any noise generated by other phones, fax, answering machines and analog modems introduced by the Plain Ordinary Telephone Service (POTS) line while passing high frequency signals to DSL Modem. The DSL Phone Splitter isolates DSL and home phone line signals from voice signal on both lines for peak data performance and voice quality. The filters block the on-hook phones from degrading the DSL digital modem signal effectively.