RJ11 Socket in dash - What's it for?

[Stenasev]

Just bought a vehicle that has a non OE rj11 socket in place of the cigarette lighter socket. Traced it back and it leads to a box that has the usual battery, ignition and earth connections. Also loops into the radio aerial, i.e. original aerial lead plugs into the box and another come out to go to the OE radio. There are no visible markings on the box.

I don't think any of it is vehicle specific but it's a 2003 Jeep Cherokee.

I'm guessing some kind of FM modulator or maybe CB radio related as found an unconnected CB antenna connector behind the dash as well.

Any ideas?

[a7x88]

Some sort of primitive car phone? A handset that plugged into it or something?