The first telephone exchange was not until 1881 in Arizona territory. This film states it starts out in 1879 Arizona territory, so the telephone would not have been there yet.
When Michael and Angel are gathering their guns and ammo after they have decided to help the two women, and the shot zooms in and shows the rounds cascading to the table in slow-motion, none of the rounds have primers.
Around the 19 minute mark a vehicle can be seen driving down the road in the distance.