GSM vs. CDMA – Which Network Will My Phone Work On

I see tons of questions asking if certain cell phones will work with certain carriers. I’m hoping that this little write-up will help answer those questions and give you a little more knowledge about the two prevailing technologies.

Lets start with Global System for Mobile Communications or GSM. GSM is a standard that was setup in Europe. GSM was non existent in the US until recently. GSM has started making major inroads in the United States recently. To help boost the speed of GSM technology EDGE, UMTS and HSDPA were created. Each standard has a higher upload/download speed then the next. EDGE has a speed of 70-140 kbps. UMTS and HSDPA have speeds of 275—380 kbps.

In order to use the GSM network in the United States you need to have a Subscriber Identity Module card (SIM card). The removable SIM card allows phones to be instantly activated, interchanged, swapped out and upgraded, all without carrier intervention. The SIM itself is tied to the network, rather than the actual phone. Phones that are card-enabled can be used with any GSM carrier. With GSM you are able to switch from one carriers GSM network to another without any problem. For example if you take your GSM phone to Europe you can automatically get connected to GSM carriers in Europe without signing up for contracts with those carriers. The only catch is that your phone will need to be a quad-band GSM phone. Meaning your phone works on 850/900/1800/1900 MHz frequencies.

The US carriers that use the GSM network are AT&T and T-Mobile.

Now lets look at Code Division Multiple Access or CDMA. CDMA is a standard that was established in the United States by Qualcomm. CDMA is always used in parts of Asia. To help boost the speeds of CDMA, EVDO was created. The download speed of EVDO claims to be about 2 megabits per second.

A R-UIM card is the equivalent to the SIM card, R-UIM cards are only available in parts of Asia but could someday make it to the United States. CDMA carriers in the U.S. require proprietary handsets that are linked to one carrier only and are not card-enabled. To upgrade a CDMA phone, the carrier must deactivate the old phone then activate the new one. The old phone becomes useless.

The US carriers that use the CDMA network are Sprint, Verizon and Virgin Mobile.

That just about sums it up at a very high level. If you have a phone that takes a SIM card it isn’t going to work on Sprint, Verizon and Virgin Mobile. On the other hand if you have a CDMA phone it won’t work on AT&T or T-Mobile. It’s as simple as that for now.

Oh yeah, one last thing. Often with GSM you hear a lot about unlocked phones. An unlocked phone means that the phone is locked to only work with the a particular carrier. If you unlock the phone then the phone will work with any SIM card on any GSM carriers network. So if you buy a Nokia that is only sold in Europe and not by T-Mobile for example, you can unlock the phone and use your SIM card to allow it to work on the T-Mobile network. Unlocked phones does not pertain to CDMA phones as noted above.