The Term Unlocked is meant for Cellular Phones which have not been subsidized and Locked by any Wireless Services Provider, therefore, unlocked phones can work with any GSM Wireless Service anywhere in the World. 

GSM is a Wireless Platform and the technology that carries the signal back and forth from the phone to the receiver (Receiving Towers). 

Unlocked GSM Phones will only work on GSM Platform that means that your Wireless Service Provider has to be a GSM Service Provider. In the USA, T-Mobile, Cingular GSM and AT&T Digital GSM are the popular companies that use GSM Technology to provide Wireless Services to their end users.

SIM Card , also called the Smart Card is a small chip that contains your wireless service account information. You can insert the SIM Card into any unlocked GSM phone and instantly transfer your phone number and account to the new phone. If the Phone is locked, it may not accept your SIM Card.

Tri Band is a Term used for Phones that will work with 900/1800/1900 MHz Frequencies.

The Popular Frequency in USA is 1900 MHz . 

In Europe, Australia, Asia and Africa , the popular frequencies range between 900-1800 MHz .

South America and the Caribbean's have a mix of 1900 along with 900/1800 MHz. 

A Good source to check for what frequency Maps in a certain region is the web site by GSM association. Click here to see the Maps . 

Case Study of World Travel.

Lets say, you live in the USA and your service provider is T-Mobile. You are planning to travel to UK this summer. Here is how you can save yourself some bucks. 

Step1 : Purchase a GSM Unlocked World Phone from Our Online Store and use it with T-Mobile services.

Step2 : When you travel and arrive in UK, buy a local prepaid SIM Card (Range $10 - $30) from any wireless store over there and insert the SIM Card into your Unlocked Phone. Change the frequency (by going into Menu Options and Network Options) on your phone to 900/1800 MHz and start using your UK Local Phone number over there for local and international calls. Local Calls will not cost you more than 20-30 cents/minute if you are using a local UK Phone number. If you Roam on your American Phone number, please expect to pay somewhere between $1.00-$3.00/minute.
This procedure will save you tons in communication cost within foreign countries. 

To View our Unlocked GSM Phone Catalog, please visit our Online Store

Cell Phone Carnival.com carries various unlocked World Phones which will work with AT&T GSM Network, Cingular GSM Network and T-Mobile GSM Network. If you are planning to travel to Europe, You can buy an Unlocked Phone from Our Online Store and use it with any European SIM Card. Same Rule applies for Most Asian, Latin and African Markets. If you require further help, Feel free to call our friendly Sales Staff at 1-800-569-8486.

To View our Unlocked GSM Phone Catalog, please visit our Online Store