You often see unlocked phones on eBay. Recently, a family member purchased one of these and there was confusion about it. Before defining this term, it is important to understand a couple pieces of background information.

  • Cellular Network Technology – The concept of unlocked phones only applies to GSM based cellular networks. In the US, there are two predominant cellular network technologies – GSM and CDMA. Both Cingular and T-Mobile use GSM which is also the standard used in Europe while Verizon and Sprint use CDMA. If you have a CDMA phone then this does not apply to you.
  • SIM Card – In a GSM network, your subscriber information is contained on a SIM card. A SIM card is a little smart card that is inserted into your phone and identifies you to the cellular network. The interesting thing about the SIM card is that it is removable and so changing a phone in a GSM network could be just as easy as swapping a SIM card. of course the SIM card is network specific so if you change carriers(e.g. move from Cingular to T-Mobile), you will need a new SIM card. If you are wondering where your SIM card is, it is typically hidden under the battery or in another similarly protected space.

Now that GSM and SIM cards have been defined we can talk more about phone unlocking. First, it is also important to mention that telephone frequency used by T-Mobile and Cingular phones are the same and so a phone that works on one network will also work on the other. As previously mentioned, swapping a phone in a GSM environment should be as easy as swapping SIM cards, and this is mostly true but there is an issue. When selling phones, carriers typically lock their phones so the phone will only work on their network. (Note that the phone has the technology to work in the other network, but the lock prevents it from being used.) Thus say a Razor from Cingular which could easily work in a T-Mobile environment will only work with Cingular since it is locked to Cingular’s network. The lock is a software configuration and the hardware is identical to that found on the T-Mobile version.

THe process of unlocking a GSM phone basically removes the network specific lock from the phone. What this means in practice is that an unlocked GSM phone can be used on any network. Back to our Razor example, if the Razor mentioned above was unlocked that it would work equally well on Cingular or T-Mobile’s network the only difference being which SIM card is inserted. The reason why this is prevalent on eBay because sellers want to sell phones that are not network specific so they appeal to the biggest audience. The issue of locking/unlocking phones also applies to phones purchased in Europe since they also use GSM, and thus sellers are further incented to unlike phones since an unlocked phone can work with almost any GSM carrier in the US or Europe.

On a side note, if you want to unlock your phone, there are a number of companies that will do this for a fee. A quick Google search will net you many names.

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