Final answer:
Granny is referring to a telephone, as it is a device used for two-way verbal communication and can be mounted on the wall. Other options like a radio, television, or computer do not match her description.
Step-by-step explanation:
The character Granny in the question is referring to a telephone. She describes it as a "box on the wall you could talk into and they kin hear you in Oklahoma," which matches the function of a telephone, a device one can speak into to communicate with others at a distance. Unlike radio, television, or computers, the primary purpose of a telephone is for two-way verbal communication. Radios and televisions are for receiving broadcast audio and visual content, and while computers can have communication functions, they are more associated with computing and digital tasks rather than being mounted as a box on the wall explicitly for voice communication.