CHICAGO, Illinois (Reuters) -- About one in five U.S. wireless subscribers will change carriers in the next year after a new rule goes into effect allowing them to keep their telephone numbers when switching providers, according to a survey released Thursday.

The survey also found that about 42 percent of consumers are aware of the so-called number portability rule, more than twice the 20 percent level industry observers have estimated.

The findings were detailed in a report by communications consulting firm The Management Network Group (TMNG), which conducted a survey of more than 1,000 respondents in September.

"In general, I don't believe the industry is fully prepared for what they will see," Rich Nespola, chief executive of TMNG, said.

Starting on November 24, wireless operators will be required to allow customers to keep their phone numbers when changing services. Number portability is expected to drive up customer turnover and costs as it becomes easier for unhappy consumers to switch carriers.

As the deadline nears, companies have been scrambling to head off potential damage by making network improvements, reevaluating customer service and stepping up their marketing.

Nextel Communications Inc. , the No. 5 U.S. wireless telephone company, recently announced several service agreements with other operators to cooperate on providing number portability. Verizon Wireless, the largest U.S. wireless telephone operator, has also been in the forefront in supporting number portability.

TMNG expects 30 million customers to change wireless service providers during the first 12 months after number portability takes effect. Because each request for portability must be processed by two wireless providers, the industry would handle 60 million transactions during the first year, it said. An earlier TMNG study found that about 24 percent of large businesses -- the most likely segment to take advantage of number portability -- are ready to switch services.

TMNG also found that low-end users, who are typically very price conscious, and high-end users, who are most demanding of high quality service, reported the highest awareness levels. More men were aware of the new rule than women.

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