jettredmont said:
Both. First, there are, if I remember correctly, four separate technologies at work here in the US. There are some phones which only support one of the technologies, but most are dual-, tri-, or even quad-mode phones. For instance, Sprint's network is PCS; AT&T's is CDMA; etc. I think someone over here's using GSM (what the rest of the world uses), but the coverage isn't good in general. In addition, yes, phone companies brand their phones when you buy them via software so that even if the network is the same (Verizon and AT&T, for instance, I believe both use CDMA) you can't go to a different provider with the same phone.
Well-intentioned, but HIGHLY misinformed post.
First off, if you want to know anything about cellular, start with
www.howardforums.com where all the phone geeks hang out, or
www.gsmworld.com.
Next, lets clear up some misinformation about standards.
There are 4 basic voice standards in the American market: AMPS, TDMA, CDMA, GSM. For the sake of argument, let's ignore the iDEN 'push-to-talk' business that Nextel uses.
AMPS = Analogue Mobile Phone System. Remember 'bag' phones, or the original car phones with the curly antennas? I don't know where one would even get a new AMPS phone any time in the last 4 years, but AMPS service still exists for many legacy devices still in use. This is the only NON-DIGITAL cell system in use.
TDMA = Time Division Multiple Access. Usually 800/850 MHz frequency band.
CDMA = Code Division Multiple Access. Usually 800/850 MHz frequency band.
(WCDMA and 1xRTT are the data protocols that may accompany CDMA voice service)
GSM = Global System for Mobiles.
(GPRS and EDGE are the data protocols that may accompany GSM voice service).
There are four frequency bands that GSM service may be provided over:
The rest of the world uses 900MHz/1800MHz for two bands (900MHz for shorter range with better building penetration, and 1800MHz (a 2x multiplier) for longer range with worse building penetration). These two bands were already assigned to other purposes in the USA when the GSM standard was established, so for American operations we went one notch up and started with 1900MHz. Now that GSM is taking over the US market, old cell towers are being updated. Since they used to use the 800/850 range for CDMA or TDMA, it's easy & cheap to convert them to 850MHz GSM towers. Hence, the fourth band. To recap:
850 = USA
900 = World
1800 = World
1900 = USA
So you can see that a tri-band 850/1800/1900 (e.g. the SE T616) is optimised for the US with limited international use. A tri-band 900/1800/1900 (e.g. my Nokia 6600) is optimised for world use with limited USA use. A quad-band 850/900/1800/1900 (e.g. the v600) is a true 'world phone', able to work on GSM frequencies around the world (if your carrier has roaming agreements, but that's a different issue). So, pick the phone depending on where you'll be using it. People at my company travel internationally, so AT&T service with the v600 has been a lifesaver since AT&T has the best international roaming agreements and the quad-band support means they get the best service regardless of where they are.
TDMA & CDMA phones are usually carrier-specific. You can't even own two phones and switch between them on the same account, since that has to be done by a rep for the carrier and is a pain. You're locked-in and screwed.
GSM phones will work on any GSM carrier if the frequencies are compatible. If you buy a GSM phone at a discount through the carrier, it'll be 'locked' to that carrier unless you find someone to unlock it (can be done on-line for ~$20.00, more or less). GSM phones have a slot for a thumbnail-sized SIM card. Your 'account' is in the card *not* the phone. That way, you can put your card in any unlocked phone and it'll work. You can have a different phone for each day of the week, or to match your outfit, or whatever, and simply pop your SIM card into the phone and it'll power up with your number and whatever contacts you've stored on the card.
Now let's look at the major carriers:
Assume that most of these carriers had AMPS service 'way back when', but haven't set up new subscribers since the late 90's.
AT&T Wireless: TDMA until 2002, now only signing up people with GSM service and migrating old TDMA users to GSM (like me). GSM Service initially all 1900MHz, now only phasing in 850MHz coverage. Transparent roaming on Cingular's towers where available.
Cingular: TDMA until 2002, now only signing up people with GSM service and migrating old TDMA users to GSM. GSM Service initially all 1900MHz, now only phasing in 850MHz coverage. Deal to merge with/absorb AT&T pending regulatory approval. Transparent roaming on AT&T's towers, where available.
Sprint: Proprietary CDMA network with 3G extensions, 850MHz. No signs of migration to GSM.
Verizon: CDMA with 3G extensions, 850MHz. No signs of migration to GSM.
T-Mobile: GSM 1900MHz only.
Smaller players in the US used to vary between TDMA and CDMA, depending on who they wanted to be friendly with for roaming. Now, more will be GSM as the combined GSM user base will exceed the CDMA user base.
In most parts of the US now, if someone is using AT&T, Cingular or T-Mobile and their phone is less than 2 years old, they're most likely on GSM.