RJ10

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4P4C modular connector as would plug into an RJ9 socket

Wired Telephone using RJ9

The 4P4C connector (popularly, though incorrectly, called RJ22, RJ10, or RJ9), is the de facto industry standard for wired telephone handsets. It is used to provide connection from the base of the telephone to the handset. "RJ" stands for Registered Jack, a family of telephone connection standards. This handset connector is actually not a Registered Jack at all, since it was never intended to connect directly to the telephone service lines. It uses the 4P4C modular connector, which has four pins or electrical connections per connector.

Wiring

When used for connecting handsets to the telephone base, the following wiring diagram is used.