What connection is this?

[RizzoTheRat]

I have a box in my lounge with one RJ45 and 2 of the narrower phone sockets in it.

Opening it up I found there is a Cat 5 cable coming in, with 2 wires to each of the phone connectors (right), and the rest to the RJ45 (left) with some additional resistors on the back of the keystone. I'm going to rip it out to run a couple of Cat 5e through, but I'm intrigued as to what it was. Is there another type of phone cable that use RJ45?

[LordLoveLength]

Possibly basic rate ISDN?

[Harpoon]

Home Highway had two analogue phone sockets and an RJ45 for ISDN data

[RizzoTheRat]

ISDN would make sense, non UK so not Home Highway specifically but I guess lots of people used similar technology.