Thierry wrote:
Rest the question (theoretical) to know where 'd begin K and W, on the
Mississippi or not... I think that I could find the info somewhere on the
web.

http://www.earlyradiohistory.us/kwtrivia.htm

The dividing line between W and K was originally the eastern borders of
the states of New Mexico, Colorado, Wyoming, and Montana. This was set
at a time when most radio stations were used to communicate with ships.
W callsigns communicated with ships in the Atlantic Ocean and Gulf of
Mexico; K callsigns communicated with ships in the Pacific Ocean. When
broadcasting stations came along, they received essentially the same
kind of license used by maritime shore stations, and call letters
assigned the same way.

As there came to be far more broadcasting stations than maritime shore
stations, they began to run out of W callsigns. At that point it made
more sense to move the dividing line east, and the Mississippi River was
apparently a good choice.

This applies only to broadcasting and commercial maritime stations
though. Hams within the United States (not in offshore territories)
*always* received W callsigns until after World War 2, and even after,
there was never a geographic W/K dividing line for hams.
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com