If you’ve ever needed another cell phone before your existing contract has expired, you understand the problems of buying another phone. If you go to the store you originally bought your phone from, they will try to renew your contract for another 2 years or they might try to sell you their phones at inflated prices.

Many people result to buying cellphones online and if you do, you’ll most probably run into the term “unlocked.” Unlocked basically means generic and these will work with any sim card Phones that use sim cards use GSM . In the United States, the 850/1900 frequency is used so any phone using these 2 frequencies will work. Examples of phones that will work in the United States include quad band phones and a dual band phone using the 850/1900 frequency.

But not all carriers use GSM. For example, Verizon, Alltel and Sprint are all carriers who use CDMA. Their phones do not require sim cards, so unlocked phones will not work with these carriers. To buy a phone to use with a carrier using CDMA, you would have to buy phones specifically for that carrier and then call your carrier to inform them that you want to change phones. Always try to call your carrier yourself, because some stores charge up to $70 to do this when you can do it for free.