According to S1:E12 where Cyd and Shelby try to erase GDD and end up making Cyd live in Peru and Shelby live in Alaska, Shelby's family still lived in Portland in the 3rd grade. In S1:E8, Norm says that he has been working for GDD for 12 years. Since the teens are 15 in the series (S1:E10), that means they would have been 3 years old in 3rd grade, which isn't possible.
The episode is set in 2015, and Cyd and Shelby infiltrated Janet's garage in 1991, having gone back in time 24 years, yet Janet mentions it having been 25 years.
Peru is in South America outside the United States, so Cyd and Shelby would not be able to phone each other basically, seeing what it would require to call someone internationally.