The Citizens Utility Board analyzed more than 4,400 bills and found that people over pay, on average, $359 per year.
CUB blames much of that on unused minutes and unneeded services.
To save money, the organization recommends that people who use fewer than 300 minutes per month switch to a prepaid wireless provider.
The group also advises cell phone users to check their bills closely to be sure they are not being charged for anything that they should not be charged for.
CUB offers a free online service called Cellphone saver to help advise consumers on whether they may be paying too much.