The issue of unlocking mobile phone devices is well-known within a large group of cell phone users. The idea is simple: when a mobile service provider sells mobile phones through a retailer, it makes the phone inaccessible to services of an alternate operator by "locking" it. This is reasonable only under the terms of the contract period, thus you can use services of any other operator after the termination of the contract. However, since the first provider subsidizes the cost of the phone (often heavily), it doesn't want you to take the cheap phone they paid for and then give all the service fees to some other company. That is why it locks you in with, let's say, two years of contract, so users who travel outside the country, and drop in a SIM card from another operator, find an error message on their phone, saying "Card Blocked", or "Network Blocked", or a similar message.

Some people end up by buying unlocked phones, which can be pretty expensive. However, for many, the solution is simply figuring out a way to unlocking mobile phone devices they already bought, but this upsets mobile operators to no end. A couple of months ago, one of them even had some people arrested for unlocking mobile phone devices. Still, unlocking a cell phone is not all that easy, and it seems unlikely that it's being done by that many people to feel the need to go around and start arresting them! So, this is becoming an interesting matter to discuss. However, any problem must have at least one solution, and if you haven't yet purchased a mobile phone, or are thinking of making a change, here are some important things to consider.

Basically, cell phones are radios, with frequency bands just like the AM, FM, VHF or UHF bands on your radio and TV. You don't see what frequency your cell phone is on at any given time; it's all controlled by computer chips in the phone. Different governments choose different radio bands to reserve for cell phones. In the U.S. and Canada, most phones transmit on frequencies around 850 and 1900 MHz. Europe and Africa, on the other hand, use the 900- and 1800-MHz frequencies. Latin America, Oceania and Asia relay on a mix of three or even four bands. There are even more bands used for phones in some countries, like 450 MHz and 2100 MHz, but the aforementioned four are the most popular.

Global roaming phones usually work over three bands (tri-band phones): they're either 850/1800/1900, with better coverage in the U.S., or 900/1800/1900, with better coverage abroad. It's difficult to make phones with all four bands because the 850- and 900-MHz bands are very close together, but the number of quad-band phones is growing. They provide the best coverage of all.

Even better than a tri-band or quad-band, a GSM ("Global System for Mobiles") phone is something that's difficult to come by in the U.S., as the more common type of digital mobile phone service used here is CDMA, but just about every other country in the world uses primarily or only GSM. This is also one of the reasons why Europeans use the term "mobile" and not "cell phone". For you as the user of your phone, there is no difference at all between using a phone on a CDMA system or a phone on a GSM system.  Unfortunately, the two different systems are not compatible with each other. Moreover, as far as we are aware, all GSM phones can be unlocked. But if your phone is not a GSM one, then it probably cannot be unlocked.

Thus, if you are lucky to have a mobile phone that can still be unlocked, there are two ways for you to choose from: either you key a secret code into your phone, which is usually a unique number only for that particular phone, based on its serial number (what is called its IMEI) and the service provider who locked it, or you rewrite your phone's operation system software. The last option requires connecting the phone via a special data cable to a special programming unit. For this purpose, there are a number of web sites that offer unlocking mobile phone services and equipment.

Usually, after unlocking your phone, it will sy something that sounds sort of encouraging and you will be able to use it with any SIM (Subscriber Information Module) card. Besides, you will be able to fly with it to Europe, USA, Africa, or any other part of the world, and enjoy a phone-stress-free trip. At the end of your trip you can keep the phone for next time, recycle it, sell it, or do just about anything else with it!