Regarding line calls, I do not say 'OUT' anymore when an opponents' ball is in the air. I may say 'BOUNCE IT' or 'LET IT GO' if I think it has a chance of being out. That way, my opponents cannot argue over me calling the ball out. If the ball lands in, point continues or they win the point. None of my opponents have ever argued with me about what I say. I find that if I cannot get to a ball, just stopping and keeping head still can improve line call significantly. 2 cents.
On service returns, the line perpendicular to the net should be called by the returner unless s/he is blind. The center line can be called by either. Line parallel to the net should be called by returner's partner.