Breast compression also works well to speed up pumping time (for those of us
with little patience). I actually have often found it faster to single pump
(with either an electric pump or manual cylinder type pump that you can keep
the  suction going using one hand) and compress the breast with the other
than to double pump. (This also give you one hand free to dial the phone etc)

Personal experience related hear. ( I know that you are supposed to release
the pressure on pumps to prevent nipple trauma but sometimes speed is of the
essence such as when you are not sure when your beeper will next go off)