The FCC has sent a letter to AT&T Wireless requesting an explanation for the problems it is having porting numbers to and from its network.The carrier is reportedly having the most trouble of any complying with the FCC\u2019s wireless number portability rules, which went into effect Nov. 24 and are designed to stimulate competition by enabling subscribers to change carriers but keep their wireless or landline phone number. To date, only about 250,000 subscriber porting requests have been made, according to market research firm Mobile Competency.Mobile Competency says half of those requests were not completed, but published reports state that AT&T Wireless is having the most trouble of any carrier, with a 60% failure rate.The carrier should have responded to the FCC letter on Dec. 10 with a description of the problems and what it is doing to fix them (deadline on this column precluded us from determining whether the carrier responded).AT&T Wireless acknowledges the problems and says it is working through them, but also adds that the snags are not unique to it. Indeed, Cingular Wireless said it, too, was working through some \u201cissues\u201d tying up number porting success.\u00a0Bob Egan, president and founder of Mobile Competency, says unlike Year 2000 issues, carriers did not prepare for the date-specific event of wireless number portability. As a result, a process that should, by FCC standards, take only 2-1\/2 hours is taking up to a week or longer, according to Egan.Egan says accuracy of subscription and billing data is an issue in whether a number port goes through. Information, such as middle initials, titles, abbreviations, etc., have to appear exactly as they do on the subscriber's current account before a port is successful.If a number port is not complete, subscribers are stuck paying for two services\u00a0- the one they're trying to leave and the one they are trying to go to, Egan says: \u201cIt\u2019s a mess."