When you purchase used cell phones from an online vendor, there is no need for a new mobile phone contract with a cellular provider (2 year agreement with most companies). You have the power to approach the cellular provider with phones that you buy your own, whether online or at a repair center and have the carrier activate the phone. No need to even mention a contract allowing you to move to a different provider at a later date if you choose to without paying steep cancellation fees. You can even keep your mobile phone number when doing this.

Before you go ahead and by any used cell phones you need to do some research to make sure you end up with the right phone for you. Whether you are using AT&T, Verizon, Sprint or T-Mobile one key thing that you'll need to know before beginning to shop for a used phone is what kind of technology your service provider uses.

GSM technology (global system for mobile communications) is used by an estimated 85% of the global market; making it the obvious preferred choice for mobile makers when releasing a new handset. AT&T and T-mobile phone providers use GSM technology whereas Verizon and Sprint use CDMA (code division multiple access) technology.

It is not too hard to tell one type of phone from another. GSM phones use a SIM card and CDMA phones do not. Some of the latest Blackberry phones that operate on CDMA technology can also be unlocked to be used with GSM providers. An example would be if you purchased a Blackberry storm for Verizon, you could have it unlocked to be used with AT&T and T-Mobile. If you buy a refurbished cell phone made for GSM networks, using the phone is as simple as putting your SIM card (which you get from your provider) into the new (used) phone. The phone will then be able to connect to the network that the SIM card is associated with. This is particularly advantageous for people that do a lot of international travel as you can avoid expensive roaming fees by getting a prepaid SIM card for the international network you plan to operate on.

CDMA phones are not as easy to activate and will most certainly require either a phone call to customer service or visiting your local store. The process is not too complicated but there are extra steps involved.

When choosing between CDMA vs. GSM phone providers, you want to weigh out what options you have for plans and also the phones that are supported. There tend to be more used blackberry phones available for GSM providers than GSM.

When it comes to getting the best service, both technologies offer similar levels of coverage area, call quality, and data transfer speeds. The amount of coverage you get will be dependent on your provider, not necessarily the phone that you choose. If you do a lot of traveling, make sure that you ask your provider about roaming fees, as the additional charges vary based on provider and plan. GSM phones tend to be more user friendly worldwide since you can simply purchase a sim card and place it into your unlocked GSM phone to use it.

One other thing to consider when selecting a used cell phone on a CDMA or a GSM network is if all of the features the used phone offers will be usable on the network you are researching. Some mobile providers charge extra for certain features or simply don't offer them.

And, remember to only buy used cell phones from reputable dealers (like those that offer a warranty) and/or trusted sources that have the positive feedback to back them up.