Generally I would say yes.
In my experience most people that talk on the cell phone while in the grocery check out line are loud and inconsiderate.
Too often the cashier has a question,
and the cell phone talker is unaware.
This causes the entire line to backup.
keep in mind that everyone in the line can hear your side of the conversation.
If start talking about someone,
there is a possiblity that one of the other customers in line may know that person.
Unless it is an emergency
I would say take a five minute break while checking out and avoid using the cell phone.