The short answer is, yes, they are for the most part plug and play.
Sometimes the plug part is not obvious, but if you follow the directions
you'll figure it out.

I have a similar predicament, bought a 4pl Beechcraft with an old
Davtron 202 2-place intercom that doesn't work very well. There is a
set of jacks straight into the radio, down by where the old microphone
hangs below the throttle quadrant. I have a Softcomm 4-place portable
intercom from my training days. I plug it straight into the radio and
then plug everyone in the plane into the portable, set it between the
front seats, and secure the wiring, and I'm done.

The PTT in the pilot's yoke activates the intercom's talk circuit, so
from my perspective it's just like having a built-in unit. It isn't the
most convenient unit to adjust, but once it is set I don't need to touch
it in the air. There is even a pilot-isolate function if I get
desperate or my pax get too chatty.

If I remember to turn it off, a 9V battery lasts a good 15 hours of
continual use. I think the intercom cost $160 new. It will last until
I can afford to install a real intercom and put jacks in the back seats.


GE wrote:

I recently purchased my first a/c, unfortunately it only has a 2 place
intercom. I don't really want to go through the trouble of installing a four
place intercom for the few occasions that I take backseat passengers. I have
looked (online) at the portable intercom systems but I am not sure how they
connect and if they will be compatible with my current intercom. Do these
things just plug and play? Any experiences that you can relate will be
greatly appreciated.