CLEVELAND -- Almost 140 million people use cell phones, and many of them complain about their service.

A recent survey of cell phone users showed that one-third are seriously considering changing to a new carrier.

But before you sign up with a new service provider, On Your Side Troubleshooter Chris Caswell reported on what you need to know.

Consumer Reports recently asked cell phone users in six metropolitan areas about their service.

"Cell phone users complained about spotty coverage -- dropped calls, lots of static," said Jim Guest, of Consumer Reports. "Billing problems and lousy customer service were also huge concerns."

Verizon Wireless consistently ranked at the top. But every service has dead spots and marginal coverage in some areas.

"The best way to find a company with good service where you need it is to talk to people who live and work where you do," Guest said. "Find out which service providers work best for them."

It's also important to choose the right plan, according to experts.

"Decide how you're really going to use the phone," Guest said. "Will you make most of your calls at night, on weekends, or during business hours? Pick a plan that really meets your needs."

Ask where roaming charges will apply and how much they'll be.

Also, be aware of any additional charges for things such as extra minutes, long-distance calls, directory assistance and customer service calls.

If you do decide to switch providers, a Federal Communications Commission regulation that will let customers keep their phone numbers when they switch is scheduled to go into effect in November.