Just because the customer is the one shopping, and the cashier is the one with the job, doesn't give the customer carte blanche
to act like a jackass. Somebody jabbering away on a cellphone in the middle of a transaction can be disruptive, not only to the cashier, but to other customers. It can make it difficult to serve them if they can't talk back to the employees. And it holds up the line as well. Why should those running the store have to allow that?
In the end, while it may be technically allowable to have the customer yakking away, it doesn't make it right
. All parties have certain responsibilities to each other. Job or no job.