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Cisco 827-4V ADSL Router
"Four Analog Telephone (FXS) Interfaces"
http://www.cisco.com/en/US/products/hw/routers/ps380/products_data_sheet09186a0080092162.html
FXO—Foreign Exchange Office. An FXO interface connects to the PSTN's central office and is the interface offered on a standard telephone. Cisco's FXO interface is an RJ-11 connector that allows an analog connection to be directed at the PSTN's central office. This interface is of value for off-premise extension applications.
FXS—Foreign Exchange Station. An FXS interface connects directly to a standard telephone and supplies ring, voltage, and dial tone. Cisco's FXS interface is an RJ-11 connector that allows connections to basic telephone service equipment, keysets, and PBXs.
http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/voice_c/vcprt1/vcvoip.htm
А также
FXS-FXO Converters
http://www.voip-info.org/wiki-FXS-FXO+Converters