What is a SIM Card and what is "unlocking my phone"

Sim Cards and Unlocked phones


A GSM phone is not directly linked to you|GSM phones are not binded to your device. Rather, it has a removable card, called a SIM (subscriber information module) and this Card has a unique number on it. This is what identifies you to your wirless provider


Generally cell phone service works so that the unique serial number in your cellular phones (its ESN) is used by the cell phone provider to identify you and connenct you to their network. The wireless carrier 'knows' that a particular mobile phone's serial number is your mobile phone and knows to send phone calls to that phone when someone dials your cell phone.

The important difference about this is that you can put your SIM into any compatible phone (rarely are gsm phones not compatible) and that phone will now act as your mobile phone, because sees the SIM that is tied to your account in the phone. They couldlnt care less that you've transferred phones, all they care about is if they can deliver service to your SIM
And now for the really glamorous part of this. In theory, you can transfer your SIM to any phone, the other way is also true. Any phone can communicate with any SIM card. So, if you've already bought an expensive cellular phone that you enjoy and have learned how to use, if you change from one GSM network to a new one, you don't have to shell out money for a new phone. You can keep the phone you've grown accustmed to, and all you need to do is swap the first gsm carrier's SIM with your new service provider's SIM.

But, some wireless providers 'lock' their phones, meaning that their phones have been programmed to only work with SIM cards issued by them. Repealing that programming - unlocking your mobile phone so it can work with any GSM carrier - is what this is all about.
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What is GSM Technology? Is it different than normal cell phone service? How do I know if I am on a GSM network or not?

GSM is a type of mobile phone infrastructure. The more common type of cell phone service in North America is CDMA technlogy, but just about every other country in the world uses primarily or only GSM.

For you as the consumer of your phone, there is no difference at all between using a mobile phone on a CDMA system or a phone on a GSM carrier. Unfortunately, the two different systems are not compatible with each other so you cant switch between phones if your mvoing form GSM to CDMA or vicea versa

If you have a T-Mobile or Cingular(now AT&T) then you are using a GSM phone.


Can I just buy an unlocked phone without signing up for a service agrement?

Yes, there are several ways to buy an unlocked phone without needing to sign up for a year or two of service that you mightn't need. You can simply buy a used or new GSM phone on the internet or from a friend or somewhere like that.

If you buy a used cell phone from an individual always make sure it unlocked before commiting to purchase.

You can also purchase Unlocked Cell Phones from online stores such as my favorite,J-Cellular or Best Buy