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In other words, retaining a mobile telephone number is something anyone can do, regardless of the telephone company they've been using. The phenomenon is known as portability, and to enjoy it you must take three steps.

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1.�Request portability. Go to any branch of the company you want to switch over to, and follow the instructions given there.

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2.�Provide the required data. In general, and aside from personal data, the first requirement is to fill out a form requesting your SIM card number and the telephone number you want to keep.

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3.�Provide the date as of which the portability is to be operative. This is important for people who use their cell phone often because it takes two to three hours for the updating to take place. Sometimes it can take a whole day, but this is unusual. However, the changeover is usually done in the middle of the night so as to interfere as little as possible with the customer's telephone communications.

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Changing telephone companies without losing your number is not free of small problems, which you should know about in order to waste as little time as possible. On average, companies take two to three weeks to carry out all the technical changes involved in portability.

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The first obstacle is to meet the seniority requirements of the company you are abandoning. Just over a year ago, mobile companies eager to win market share gave away terminals with the condition that the customer not change over to another firm for at least a year.

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Another problem is unpaid bills. Companies have teamed up to keep deadbeats from simply changing companies to avoid paying their debts. You must first settle up with the company you are leaving.

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Finally, giving wrong or incomplete data on the application form of your new company can delay things.

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Portability is usually free but not always. Some companies may change supplementary fees to cover processing costs. You must also pay for the SIM card of the new company in which the desired number is already recorded. As for pre-paid cards, the new company has no obligation to respect the balance its new customer has with his or her former telephone service provider.

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Meanwhile, customers who want to get rid of their mobile number must follow a path almost as tortuous as the one we have just discussed. The most orthodox way is to contact the customer service office of the telephone company and ask for the mobile to be deactivated. You will be asked for data on the brand of the cell phone, how long you have been with the company, how many calls you have made since signing on and the IMEI code, which is a number written on the inside of the phone. It is convenient to have handy in order to cancel a contract or if the phone is stolen or lost. Another option, which is less above-board, is to find some person (usually on the black market) who knows the codes to free up terminals. This is a fast system although it costs 15 to 20 euros and includes no guarantees.

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If the problems associated with portability are too messy, users can turn to different government bodies such as the consumer affairs office in their region or city or the National Commission for the Telecommunications Market (tel: 91-372-4149). Or you can go to court. You can also resolve a lot of problems by consulting with the mobile telephone companies themselves, such as Telefonica M�viles de Espa�a (tel: 1485), Vodofone (tel: 607-123-000) and Amena (1470).