thanks, Arcforce...
i guess you're right, the net-guy shouts "net" for the umpire to know that the ball on serve touches the net and a "Let" should be played.
what really intrigue us is, what brought about the use of the word "Let" whenever we want to replay a game because of allowable hindrance; ball touching the net during serve, an errant ball from adjoining court rolls over our court; etc.