When Edith takes the pie shell out of the oven she has a red potholder in her left hand and a yellow one in her right. In the closeup shot of the pie shell the potholders are reversed.
Mike, having the Rempley's full names and address from their letter to Edith, could have tried dialing telephone information first for their phone number, before sending a telegram to them, which arrived too late. The Remplys, who lived in New Jersey, arrived within only a minute or two after Mike & Gloria left. So even if Mike had been able to reach them by phone, there would've been no answer, as they were already en route to the Bunker's house.