How do I change my GSM at&t phone to a CDMA cricket phon
CDMA is Code Division Multiple Access, which can actually describe several different radio technologies, but usually when someone says CDMA they’re referring to Qualcomm’s CDMA2000 system, which is used by Sprint, Verizon, and Alltel in the US, as well as a few other companies in Asia and South America.
There are some interesting technical differences which I’ll describe below, but as a customer, you mainly only need to worry about GSM vs. CDMA if you’re buying a phone from eBay or something. Make sure if your carrier uses GSM, you get a GSM phone, and vice versa. Many phone models have both a GSM and a CDMA version, but some are GSM only or CDMA only.
GSM separates calls into frequencies and time slots. (This is called Time Division Multiple Access, although there’s another incompatible system just called "TDMA" that Cingular and AT&T used to offer.) When you make a call, the network tells your phone to use a certain frequency, and broadcast at a certain time within each second. CDMA, on the other hand, has everyone broadcasting on the same frequencies simultaneously, but each call is encoded with a different code, and the network is able to pick out each call by knowing its code - just like you can pick out one person's voice in a room with lots of people talking. copyright ybarra-cgm
One effect this has is on how the network deals with overloading. With GSM, there are a fixed number of frequencies, and a fixed number of time slots within each second, and when those are all full, the system simply can’t handle any more calls. All the calls that are already going on will keep working, but no new calls can be made.
With CDMA, there’s no hard limit on the number of calls, but there is a "soft limit" (which I believe is usually higher than GSM’s hard limit). Since everyone is on the same frequencies, each call makes the others a little harder to pick out. As more calls are added, what happens is the effective size of the cell shrinks - just like how in a quiet room, you can hear someone talking all the way on the other side, but as it gets noisier, you can only understand the people right next to you.
Another difference has to do with moving between neighboring cells. With GSM, the calls on one cell can’t use the same frequencies as calls on a neighboring cell, because the broadcasts would interfere. This means the radio spectrum can’t be used as efficiently. But with CDMA, everyone’s using the same frequencies anyway, they just have to use different codes (and there are plenty to choose from). Because every tower and handset uses the same frequencies, your phone can talk to a far-away tower at the same time as a closer one, which makes it less likely for the call to be dropped as you move.
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CDMA is fundamentally a better technology than TDMA/GSM, which is why all the 3G systems use Code Division Multiple Access (even though they’re not all compatible with "CDMA" as used in the US). But GSM has the advantage of being an international standard that’s been in place for many years, so you can use any unlocked GSM phone with any carrier in any country. GSM also uses "SIM cards" to store your account information and contact list, so you can switch phones just by taking a chip out and putting it into the new phone, and when you travel, you can buy a prepaid SIM card from a local carrier.
I guess I needed to elaborate in my answer about K1 phones. Well, I'll do it here.
GSM and CDMA are two different communication standards. All U.S. providers use exclusively one or the other.
GSM means "Global System for Mobile communications", and it is the standard currently in use more or less worldwide. In the U.S., the major providers using this standard are T-Mobile and AT&T Wireless. ybarra-cgm.com
CDMA means "Code Division Multiple Access". This standard used to be the dominant standard in the U.S. Now it is used by Verizon and Sprint. It still has more users than GSM, but the difference is not very significant.
Historically, CDMA was developed by Qualcomm, made a U.S. standard, and gained some acceptance before GSM became established; however, once GSM was created, all countries without established CDMA networks accepted GSM - this is the reason why CDMA is almost non-existent anywhere but USA and Japan.
From a user's point of view, the actual standard is not really important, with two caveats: first, you can't use a phone that uses one standard with the provider that uses the other standard; second, if you travel internationally, a GSM phone is almost a must.
Source: http://askville.amazon.com/SimilarQuestions.do?req=GSM-CDMA-terms-cell
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