It is possible command from "Run Basic Script" block to play a message?

Something like:

IF @A=1 THEN PLAY(MSJ01)
ELSIF @A=2 THEN PLAY(MSJ02)
ELSE PLAY(MSJ03)
END

or

CASE @A=01 THEN PLAY(MSJ01)
CASE @A=10 THEN PLAY(MSJ02)
CASE @A=11 THEN PLAY(MSJ03)

Not at present. All of the available functions for the Run Basic Script step are in the help, and are all what we would refer to as "programming functions" as opposed to audio or media functions.