There's a lot of buzz about unlocked cell phones, especially since the release of the Apple iPhone. eBay is littered with “Unlocked” phones but the reality is a lot of people don't know what an “Unocked” phone is, if they need one, or in a lot of cases, if they have one. This article will explain the basics.

When you buy a cell phone with a service plan, whether you buy it from the carrier or from a retail location, more likely than not the phone is “Locked”. This means that they phone can only be used with one carrier. So for example if you purchase a phone to be used with your AT&T service, it cannot be used with any other carriers like T-mobile. If the phone is “Unlocked” it means it is not tethered to a specific carrier, but.

Why are they locked in the first place?

When you buy a phone with cellular service, the service provider subsidizes the cost of the phone. That is why you are able to buy a phone the retails for $300 for $9.99. When the carrier foots the bill, they want to protect their investment, and make sure you don't just use them for a cheap phone and then jump to their competitor. They do this in two ways, by making you sign a contract, and by “Locking” the phone they paid for.

Is my phone compatible?

Buying an unlocked phone does not mean you can use it on any carrier. There are factors that play into the phones compatibility with different carriers like the network technology, and the frequency.

The most important consideration in choosing an unlocked phone is what network technology the phone uses. The major technologies are GSM, CDMA, and iDEN. In the US AT&T and T-Mobile use GSM, Sprint and Verizon use CDMA and Srint/Nextel uses iDEN. The important thing to note is phones cannot be used across different technologies. So if you have an unlocked GSM phone, you will not ever be able to use it with Verizon or Sprint.

The next thing you need to take into consideration is the frequency band the phone picks up and what frequency band you provider uses. The major GSM frequencies are 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz. A dual band phone will have the ability to broadcast on two of these frequencies, while a quad band phone will be able to do all four. Choosing a phone that is not a quad band is difficult because each carrier may deploy different frequencies in different areas.

I ran into this problem when I purchased an Unlocked LG Chocolate. I purchased the LG KG800 Chocolate which is a Triband phone that operates on 900/1800/1900 MHz bands. My carrier was AT&T, who in my area uses both the 850 MHz and the 1900 MHz. The phone worked with my carrier but my reception was poor because I was only able to pick up the 1900 MHz signal, while I was able to pick up both with the phone I got from AT&T.

The phones frequencies are usually published in the specs and on the box, but it can be more difficult to determine which frequency your phone is using. You can call you carrier and ask them, and they should know, however, some customer service reps will have no idea what you are talking about. In that case you can visit GSMWorld.com and look at coverage maps.

How do you unlock a phone?

There two types of Unlocked phones out there: phones that have been “Factory Unlocked”, and phones that have been “After-market Unlocked”. “Factory Unlocked” phones come direct from the manufacturer unlocked. This is the most reliable way to get them however, you will end up paying full retail price. If these phones are even available, they will be sold by the manufacturer and by retailers. The other method of unlocking involves hacking the phone. This is usually done by executing a software patch, but in some cases involves modifying the hardware (e.g. George Holtz iPhone Hack). There are usually merchants online that offer both the unlocked phones as well as a service to unlock your phone for you. Some will even sell software to unlock the phone yourself, but buyer beware, sometimes this is very complicated.

Is it legal?

The simple answer is yes. The law governing this issue is the Digital Millennium Copyright Act (DMCA). In November of 2006 the U.S. Copyright Office made an exemption to the DCMA allowing subscribers to unlock their phones. What is not clear at this point is whether this exemption allows third parties to unlock phones for resale. So while it is legal to unlock your own phone, it may be against the contract you have signed with your provider, and it may pose some other problems but it is by an large an accepted practice.

What problems?

Well if you use an unlocked T-Mobile phone on AT&T, you may not be able to use some of the T-Mobile features that come with the phone, and in the same vein the phone may not be capable of using some of AT&T's network features.

Also, by unlocking a phone there is always the chance you could “Brick It” (render it useless) or a future update of the phone may be incompatible with the unlock and it may be inadvertently bricked. All phones and carriers are different in this respect, but you should be able to find potential problems by searching forums on the net.

Bottom Line:

Unlocked phones are a widely accepted commodity and a great way to get the phone you want without having to switch carriers but it is important that you do your research and know why you are buying otherwise you could end up wasting a lot of money.