Verizon Wireless and Nextel Communications gained the most customers when wireless phone number portability went into effect last week.

PORTABLE NUMBERS Want to switch wireless providers and keep your number? Remember: Service must be on to switch -- don't cancel old service and then call new company. Your service agreement still applies; early-termination fees may apply Your phone may not work with a new carrier More tips Plan To Switch? New Cell Phone Rules In Effect

RCRnews.com reported that Cingular and AT&T lost customers.

Sprint PCS and T-Mobile apparently came out about even, ending up with about the same number of customers as they had before the rule change.

The site also said that RBC Capital Markets telecommunications analyst Jonathan Atkin said that fewer than half of the attempts to switch that he monitored were completed, and some took more than four days.

Wireless companies had said it would take about 2.5 hours to change carriers.