GSM SIM card:  Unlocked phone Vs Locked phone

There is about a dozen type of mobile phone services.  One of them is GSM (Global System for Mobile Communications).  GSM phone service provider such as T -Mobile, Cingular, and AT&T uses a smart card.  It's about half the size of a standard .39 cent stamp.  The key is that you can remove it from the phone.  The smart card or SIM card is what the GSM provider sees regardless of the phone model.  Your account is located in the SIM card.  Your address book is in the SIM. 

Once you signed a two contract with Cingular or T-Mobile you will get a locked GSM phone.  The providers do not refer to their phones as locked phones.  Matter of fact, most people do not realized that the phones only work with one provider.

On the other hand, an unlocked phone will work with more than one provider.  This is good because you can simply swap the SIM card and you can make calls in two seconds.  So, if you have seven unlocked phones and you have grown to like all of them than you can use them with Cingular, T-Mobile, Fido, Rogers of Canada and the majority of the international wireless providers.  More importantly, you can use a different phone per week and you do not need to contact the provider to activate the phone.  Very nice...Ah?

If you have a Verizon's phone than you will be using that one particular phone for the duration of your two-year-contract.  Let say your Verizon's phone was dropped in the toilet and is totaled--you will have to buy a new phone at retail price and call Verizon customer service to activate the new phone.  Verizon will likely charged you an activation fee.  

Let say my unlocked Cingular branded cell phone was ran over by a truck and the T-Mobile's SIM card was not damaged.  I simply buy a new unlocked phone or T-Mobile locked phone and insert the undamaged T-Mobile SIM into the new phone.  Power phone ON, two seconds later I can make calls.

It is wise to buy unlocked GSM phones:

1. Over 200 countries uses GSM SIM cards.  GSM is growing very fast.
2. It has over 1.1 Billion Users in the World! 
3. If you travel overseas you do not need to buy a new mobile phone.
4. If your Verizon's phone become dead than all data including the phonebook is gone. 
5. With a GSM phone, your phonebook is in the SIM card and so even if your GSM phone is dead you can still retrieve the data.
6. Convenience and ease of switching between cell phones.

So an unlocked GSM phone offers convenience and the flexible to switch phones in a heart beat.