jimI tried researching this online, but what I found was inconclusive - "26. Service calls by serving team. Neither the server nor server’s partner shall make a fault call on the first service even if they think it is out because the receiver may be giving the server the benefit of the doubt. There is one exception. If the receiver plays a first service that is a fault and does not put the return in play, the server or server’s partner may make the fault call.
So here's the situation: while playing men's doubles (a friendly game, not league) I inadvertently called my partner's first serve out as I was very close to the net and clearly saw it on the wrong side of the center line. The receiving player had hesitated and then ended up hitting the serve in to the net, with no call from his partner. I admitted that I was wrong in calling a ball on their side of the net, and the receiver admitted that he too thought that the serve was wide and out, though I'm not sure if his hesitation was because the ball was actually out or because I called it out. (Yeah, I know players that will come to the net and smack a winner that was obviously served out and then say it was always their call! If it's a return winner then they claim it was in, but if they hit it out or in the net they claim that the serve was obviously out.) So I then said second serve, and they said "Hold on, by me calling it 'out' that that was a hindrance and they wanted the point." If both sides agree that the first serve was out, then how could there be a hindrance and shouldn't it just be a second serve?