BEND, Ore. (CNN/Money) – If the hassle of changing your cell phone number is the only reason you've stuck with your wireless carrier, you may want to start shopping for a better deal.

On Monday, the Federal Communications Commission's (FCC) "local number portability" rule goes into effect in the 100 largest metropolitan areas in country, giving cell phone customers the option of keeping their number when they switch carriers within the same geographic region. (The deadline for the rest of the country is May 24.)

Customers of old-fashioned wireline phones, meanwhile, will in most cases be able to "port" their home phone numbers to a cell phone, and vice versa.

Not only will telephone users get to keep their phone numbers, they may very well see better rates, terms and service as carriers scramble to deal with a new dose of competition.

"We think the market will change quite a bit," said Bill Hardekopf, CEO of CellUpdate.com, a site that compares cell phone plans.

But the best deals may not come right away, said Adam Goldberg, policy analyst for the Consumers Union. "It may take some time for carrier to really understand the new competitive environment."

Until now, as cell phone customers know too well, you couldn't take your phone number with you when you switched carriers. Rather than deal with changing phone numbers, many customers stuck with their carriers even if the cost was high and service was lousy.

Now that customers can take their number with them, say the plan's proponents, carriers are expected to step eventually forward with:

Better stuff. New phones, with advanced features and lower prices, are sure to keep coming. Superior gadgetry -- think picture phones -- is an ever-popular enticement.

Better prices. Free months or banked minutes may be waved in front of both new and existing customers, along with other financial enticements yet to be invented.

Better terms. Contracts with steep termination fees are another barrier to dumping a carrier. Carriers could initially roll out longer contracts with higher termination fees, but may compete over the long run by offering fewer binding contracts. "It's going to be hard for carriers to stick with a system that punishes consumers," Goldberg said. "Consumers just won't accept that."

Better service. The Management Network Group (TMNG) estimates that the turnover of personal cell phone users will jump from about 3 to 20 percent in the next 12 months as a result of portability. To stem that churn, companies will have to be, well, nicer.

Before you rush to switch carriers, first see when your existing cell phone contract expires. The average cell phone has a $175 termination fee, according Hardekopf, who recommends waiting out your contract if you can.

You might also consider holding off while carriers work through inevitable hiccups in the process.

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"It's a complex process with lots of systems interfacing with other systems," said Cathy McMahon, an executive for wireless portability at Telcordia, a software company that is handling number switching for seven of the eight largest carriers. "There are places where things could go wrong."

Though Telcordia has been testing the system for more than a year, potential glitches could arise if, for example, customers give inaccurate information about their old plans. For this reason, it's a good idea to bring your old cell bill with you when you go to a new carrier.

Once you do decide to port your number, make sure you don't quit your existing carrier until you're signed up with a new one. In order to transfer your number to a new service, the new carrier needs to do the switch for you.

The new carrier will need to validate information with the old carrier and notify a centralized system, but all told, the process should take less than three hours, according McMahon. Wireline-to-wireless transfers will take several business days.

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So what will all of this cost you?

The FCC has said that carriers can also charge a fee to departing customers who want to port their numbers, though it's likely that new carriers will offer to cover the cost of switching as long-distance carriers often do.

That's not to say that portability is free. Wireless customers have actually been paying for the change for nearly two years in the form of a local number portability surcharge, typically around $1, levied on their bills.