Almost 140 million people use a cell phone, but if you ask people about their service, you'll generally hear plenty of complaints.

A recent Consumer Reports' survey of cell phone users showed one-third were seriously considering changing to a new carrier. There are some things consumers need to know before switching services.

Consumer Reports recently asked cell phone users in six metropolitan areas about their service. Consumer Reports spokesman Jim Guest says that there was a litany of complaints.

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

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

So how can you find the right carrier?

"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. Find out which service providers work best for them," Guest said.

It's also important to pick the right plan.

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

When shopping for a plan, 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. Those charges can significantly increase monthly bills.

While cellular service is far from perfect, Consumer Reports says that doing your homework will help you sign up with the best carrier for you. It also recommends asking if there is a trial period. Most will give customers two weeks to make sure the phone works where they need it.