We don't have a
house manager, but the person in charge of tickets usually has a walkie-talkie we can communicate with... Ironically, I'm usually the one as LB op who gives the call to start the show (by flipping the house lights switch off... yes, switch. No Dimmers.) Of course, as I give a countdown, I'm checking with the stage crew and tickets/ushers to make sure we can start. We have atomic clocks all over the building, so we use those to coordinate time.