The RJ12 connector is a phone that has the same dimensions as the RJ11 connector, the difference is that it has 6 contacts, instead of 4.

This connector is for a cable crimp wire 6 and has 6 positions (where the blades are housed) and 6 contacts (6P6C), implying that all are used.

The RJ-11 is mainly used to link telephone networks connector. It is small and has four contacts measures to support 4-way 2 cables. It is the most widely used globally for connecting conventional telephones, which generally tend to use only the two central threads to a single line or a twisted pair connector. And the four wires are used only for telephony equipment special using double line or two telephone pairs. After crimp the cable, it is almost impossible to disarm the RJ-11 without causing its deactivation.