It appears that
Saul was his "circumcision name" and that
Paul may or may have not been given to him as a "liaison name" for use with non-Jews.
According to a Catholic encyclopedia site (for what its worth)(http://www.newadvent.org/cathen/11567b.htm) he was given both names
Saul and
Paul at birth, but opted for
Paul (
Pavlos) because the Greek adaptation of
Saul (Savlos) indeed had ludicrous connotations (as I pointed out above).
Poor joke alert: It is possible that
Paul had held on to
Saul, the spread of Christianity could have failed, at least in areas where Greek was the *lingua* *franca*. In the same vein, had
Ralph Lipschitz not changed his name to
Ralph Lauren, maybe very few English-speakers would be prorting shirts with polo ponies on them :)