AFAIK, you're correct.

The service, which ran $19.99/month, was called "Flexphone" by SBMS.
It was really designed to allow someone with a car-mounted phone to
also take calls on a handheld when out of the car.  When the
conversion to digital came along, flexphone went away, since it lost
it's "raison d'etre".

But the two phones couldn't call each other, IIRC, since by calling
"yourself" the call would go right to voicemail.

I've got to hand it to you, John- you solved the mystery of the ages-
you figured out how to give your wife the safety and security of
wireless, yet render her incapable of calling you!  Kudos!  ;-)

I always wondered about the roaming restriction.  I suspect since
other carriers didn't support flexing, they could only authenticate
one ESN with a given number?

While it's sad that flexphone went away, the advent of cheap family
plans makes the limitations of flexphone less desirable.  Flexing can
be pretty much simulated with a family plan and conditional call
forwarding, without the roaming limitations or inability to call each
other.

Yep, I had it for a year or so.  The statement "inbound calls were
answered by the first send button pressed" didn't happen though.  The
call went to the first phone THAT RESPONDED TO THE TOWER--the other
phone would not even ring.  The built-in 3 watt mobile phone on my boat
with external marine antenna almost ALWAYS beat the other one unless I
was practically sitting under a tower.  I therefore had to remember to
turn off the boat phone when leaving.  After having to make a special
trip back to the boat several times to turn off the phone because I
couldn't receive calls I finally switched the boat phone to a 2nd number
on the same account and used call forwarding when there.