I have been in the mobile industry since I was about 12 years old (I’m 19). My passion for cell phones began with the help of my 2 brothers that worked at T-Mobile. Also, the introduction to international phones caught my eye.

I have used many cell phones as well as buying and reselling them. The knowledge in the cellular industry helped me later on in life when I began to work at T-Mobile, instead of being the “new guy”. I knew more things than the manager himself! Here are the differences that I know between the network technologies of America.

GSM (Global System for Mobile Communications)

I love the GSM network more than the CDMA network. The GSM network is worldwide and is preferred around Europe and Asia.

GSM phones use SIM cards. SIM (Subscriber Identity Module) contains all the information about your phone number, carrier, etc. It is the brains of the phone. SIM cards are unique by their number. (T-Mobile’s SIM cards begin with 890126 while AT&T uses 890141) The SIM card is attatched to your account and it is the recognition of who you are. In other words, your SIM card is your ID for your phone.

GSM phones carry unique serial numbers. The IMEI (International Mobile Equipment Identity) are on all GSM  phones. The carrier can recognize what phone you are using by its IMEI. For example, the T-Mobile HTC HD2’s IMEI begins with 357779031xxxxxx. Carriers can block out IMEIs from the network (Highly Unlikely though) if the phone is stolen,lost, etc.

GSM phones allow swapping different phones in a breeze. For example, I had the Nokia N97. I purchased the Nokia N8 and I put my SIM card in it. I didn’t have to change anything or add anything to my account. (My phones that I purchase are Factory Unlocked.)

Unlocking GSM phones can take 10 seconds. Many GSM phones can be unlocked by an unlock code, which can be obtained by the carrier the phone is used for and that you have a good standing account with them. For example, I can get a T-Mobile Blackberry Bold unlocked from T-Mobile (for free) if I am using the phone under my number. However I cannot request an unlock code from my carrier for a non-compatible phone. For example, if I have a LG Shine from AT&T, I cannot ask T-Mobile for an unlock code. In other words, I’d have to purchase an unlock code for the phone. The iPhone is unlocked via software, which is not very common for phones.

CDMA (Code Division Multiple Access)

CDMA carriers in the U.S. are mainly Sprint, Verizon, and U.S. Cellular. Verizon is the largest CDMA carrier in America, but its parent company, Vodaphone (in Europe), is a GSM company. (Weird right?)

CDMA phones have ESNs instead of IMEIs. ESN (Electronic Serial Number) is basically the same thing as an IMEI, but stolen/lost phones have a “Bad ESN”. Bad ESN phones cannot be reactivated with the same carrier. For example, if you purchase a stolen Sprint Evo, it will have a Bad ESN and therefore Sprint will not allow you to reactive it. If you want to purchase a CDMA phone over Craigslist or eBay, get the ESN first and contact the carrier to see if it is clean.

Changing CDMA phones isn’t fun. CDMA carriers charge about $15 or so to change phones EVERY time, it is not a one time fee. So don’t break your phones that quick! $15/phone can add up real quickly so if you are one of those people that break phones or change phones every week or so, DO NOT GO TO A CDMA CARRIER!

IF you want to “unlock” a CDMA phone, you need to “flash” it. You can flash phones with Bad ESNs to other carriers. Flashing phones are quite expensive and risky. If you mess up or the battery dies, your phone is now an expensive paperweight. Flashing phones take some time. You cannot flash a CDMA phone for a GSM carrier and vice versa.

So there you have it. I hope this helped you out on whether to decide to choose a CDMA carrier or a GSM carrier. I see more negatives with CDMA than with GSM. If you are one of those people who are going to hop on with Verizon to get the Verizon iPhone, think twice again. I oppose AT&T and I am happy with T-Mobile (best carrier in the Chicago Market), but I would rather choose AT&T over Verizon. It is all up to you to choose what you want.


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