Is there any standard for modular phone connectors? I suspect not since was looking up the 4p4c headset jack (referred to as RJ9, RJ10 and RJ22), I don't recall that any of the manufacturers indicated pin numbers. Of course, it also is complicated by whether the connecting cable is 1:1 or cross-over. RJ11 is often confused as it is wider and though has also 4 circuits connected, is actually spaced for 6 circuits.
Was connecting up a demo board this morning that used the 4p4c modular connector for the CAN bus. Cannibalized a connector and cord from an old telset. Became a smoke generator inadvertently. Luckily, no damage and all worked after I mirrored one of the sockets. The telco handset cord was cross-over type and luckily had enough impedance to get hot rather than killing anything else (5V and ground in it).