Novice Question: GSM v. CDMA v. TDMA (ATT or T-Mo)

[logologue]

I'm new to this forum, and not too knowledgable about cell technology, and am hoping someone can provide a little information and perhaps some advice.

I'm an ATT customer in the SF Bay Area and my handset is basically dying. Naturally, I have to buy a new phone, and am consiering switching carriers. T-Mobile has that great deal right now, but I've read various views on their coverage issues in this forum. So, at the risk of inviting another long series of postings about ATT v. T-Mo, any advice about their relative merits for my coverage area would be appreciated; I live in the Mission District in SF and commute daily to Palo Alto, usually on 280 but sometimes in the train (101 corridor), and spent a fair amount of time in the East Bay, and occasionally some time in South Marin, and sometimes Santa Rosa (well, and every couple of months in westside LA, via the 5)--personal experiences in those coverage areas would probably be most useful.

(As for the handset itself, any advice on good, moderately-priced models would be appreciated, too. I suppose text msg. capability would be nice, though I doubt I'd use it much; email/www access are both unnecessary.)

Now for a larger area of my utter cluelessness: can anyone explain and distinguish between (in some clear way, one hopes) TDMA, CDMA, and GSM? I have the impression GSM is newer and that CDMA is kind of a current standard, but can't tell if that means GSM will eventually be the standard or something; in the meantime, should I get a handset that can work in either mode (if this is even possible)? And any explanation of what these different acronyms really mean (not just what they stand for--I checked the glossary, which didn't tell me much) would also be great, just to satisfy my curiosity.

Sorry to go on for so long--I'm trying to be specific enough to make this posting and its responses as useful as possible.

Thanks in advance, and cheers--RJ

[Evan215]

I don't live in CA... so I can't help you out with the area questions. But I can help explain the technology questions. GSM = Global Standard for Mobile... and is most commonly used overseas in Asia and Europe... but AT&T just upgraded to it and T-Mobile/Voicestream and Cingular have been using it here in the states for awhile... with GSM most people often say they get clearer calls and better features. TDMA = Time Division Multiple Access... hmm I actually don't know anything about this technology because I've never had it! But I think it is somewhat similar to CDMA and AT&T and Cingular have this, as does Verizon. CDMA = Code Division Multiple Access... this is probably the most common wireless technology in the states. I personally don't like it because I think the sound quality on it stinks. Features are lagging behind on this network also. Companies that offer CDMA are Qwest, CricKet, Verizon (I think), Sprint, and probably a million other companies that I can't think of right now.

Hope this helped you (somewhat),
Evan

[tuneout]

Try here

I'd think twice before switching to other carriers though. I'm with Cingular (T-Mobile is same as Cingular) and the coverage in the SF bay area is not as good as AT&T (probably because AT&T uses both GSM and TDMA, if your phone supports it). I am not sure about AT&T's GSM-only network though.

[chefofthefuture]

I was in the same position as you a couple of months ago, with AT&T TDMA and trying to figure out what to do. The short list:

- Verizon -- More expensive than AT&T TDMA, and some people say it has much better coverage. I think AT&T TDMA and Verizon's digital coverage are similar, with Verizon having a slight edge.
- AT&T GSM -- New features, decent prices, cool phones, brand new network. Seems to have good coverage around here though reportedly not so great out of the urban area.
- Cingular/T-Mobile -- The best deals, great phones, network is now working very well in urban area, needs some improvement in fringe areas (hills in East Bay and Peninsula) and going up towards Mendocino, etc..

Ok, now an extensive T-Mobile/Cingular coverage report:

I drive 280 and 101 to Palo Alto all the time. You should be able to talk during your daily commute with little or no problem. You may get an occasional drop at Farm Hill, but just about every provider can drop there actually. One PA bummer is that there's no signal inside of the PA Fry's (ATT GSM is there though)! Haven't taken the train lately so not sure on that front. Where in the East Bay will you be spending time? I've been all over Oakland, Berkeley, Alameda and up and down 24, 580, 880 and every bridge. All of them are very solid. You might not get 5 bars all of the time, but one of the great things about the service is how well it works at 2-3 bars. I hear the UC Berkeley campus has some problems though. I do have some issues in the hills, but a buddy I was with had trouble with his Verizon phone going to analog and we kind of traded off on who had coverage at particular locations. I have noticed recent improvements near where I leave on the peninsula however.

That said, you will make some sacrifices in coverage by switching off of AT&T TDMA, major ones once you start heading towards Eureka. I was willing to live with that to get the T-mobile 1000 minute plan and their data services. If you get a T-Mobile phone and start seeing "Emergency Only" a lot in areas where you'd like to use your phone, you might want to consider AT&T GSM.

[ae101]

TDMA or Time Division Multiple Access works by dividing time among several users so that multiple users can use the same antenna or cell. For example, if there are 3 users using the same cell, for every second each user might get 1/3 of a second for transmission. That was a very simplified description of how TDMA works. I don't know how many divisions there are per second.

CDMA or Code Division Multiple Access works similar to TDMA. It doesn't give each phone a division of time. Imagine a party, where everyone is in a pair talking to each other. If everyone speaks the same language, it will become difficult to make out each different conversation. If however, every pair spoke different languages, it would be easier for each pair to speak to each other, ie one group speak spanish, one french, one english etc etc.

As for AT&T service, I've never had a drop off. In Palo Alto Fry's I've been able to make and receive calls. However there were some disruptions, discontinuities, and static in the calls. Same thing happens in the Costco in South San Fran (the one on El Camino and Hickey). I think the building may have something to do with the disruption in service. The same thing happened when I was working at US Immigration in downtown SF. However, once I left or stood next to a window at the Immigration building I get a very good signal.

[danny boi]

I live in California & use both CDMA (Verizon Wireless) and GSM (Cingular) and it's Cingular with the horrible sound; not Verizon who uses CDMA. My calls on Verizon are very clear especially when I go out to rural areas where Cingular has no service at all...Apparently you must live work and play right next to a Cingular tower...Try using your GSM phone anywhere else in the U.S...

[BizUser]

I'd say the differences between CDMA, TDMA, and GSM are not very relevant - think of it as the difference between Beta and VHS Video formats - Beta was technically superior, while VHS won out on the marketing front; and if all you want to do is watch a movie, you really don't give a hoot! I think CDMA has the best 'specs' but GSM is likely to 'win' because 80% of the world's phones are GSM (although on different frequencies than US!)... but with all networks moving to 'next generation' stuff, even this is somewhat irrelevant. As a technical aside, there are only two 'broad' digital technologies - CDMA and TDMA; the technologies of Nextel (iDEN), Cingular/T-Mobile (GSM), and ATT's TDMA (correctly known as IS-136) are all flavors of TDMA.

I think the bigger question is 'coverage', and none of the networks have great digital coverage. So what really seems to matter is a) analog fallback and b) roaming agreements. With ATT's traditional plans (ignoring their GSM rollout), you get a pretty extensive digital network (their TDMA/IS-136 network) plus a very extensive analog network, and a good number of roaming agreements. Roaming and/or using Analog can cost you dearly unless you have the right plan, but ... if part of the reason for buying a cell phone is to have coverage when your tire goes flat on highway 1 driving to Mendocino, you're more interested in getting a signal than getting a good cost per minute!

ATT and Verizon have three things going for them - a pretty solid 'base' digital network of their own; a solid analog network to fall back on if necessary (not sure who owns the analog networks); and good roaming agreements such that you can get a signal 'anywhere'. If you are tempted by the 'bazillion free minutes' you get with, eg, T-Mobile, and slogans such as 'no roaming charges', beware - you are not charged for roaming because you can't roam (T-Mobile phones are GSM only/digital only, same goes for Cingular on the west coast - different on east coast). Same goes for Nextel - no roaming is true because their phones don't work on any other network! Sprint - I know they roam on Verizon's network, but not sure if they have analog fallback capability. Bottom line is, T-Mobile, Cingular, and Sprint have fun, feature-filled phones that will likely work in major metropolitan areas and are great if you want to take advantage of cheap plans. ATT and Verizon are 'serious' networks, and their prices reflect that. Don't be fooled by the 'cheap' options from ATT - their cheap plans are very restrictive and you'll effectively have the same coverage you would get from (eg) T-mobile - except, if you "MUST' use the phone "anywhere", it WILL work (at approx. $1 per minute!).

For a graphic example of coverage, compare T-Mobile's coverage in N. California. They don't cover highway 1 north of SF very much. Then go to ATT's website, and pretend you are buying a local or regional plan, and view the coverage map. You'll see a yellow 'coverage zone', with an overlay of red-enclosed areas, denoting their own TDMA digital network. What you see is vast areas of 'yellow' that are not enclosed in red, and what that shows you is that ATT's own digital network is pretty limited - just like (eg) T-mobiles, but ... you get those huge 'yellow' areas by virtue of either roaming agreements and/or analog networks. I know the maps are 'optimistic', but ... I've driven all the way up highway 1 and kept a signal, and driven from Tahoe down to Bishop and into Death Valley and on to Las Vegas and ... I can pretty much swear that I had a signal most of the way!

I'm a long-time ATT customer and recently went through the transition to their GSM network; I bought the Siemens S46 as it was dual - TDMA and GSM. But - it has no analog capability (unlike all other ATT TDMA phones) and thus will not get a signal in many areas. I ended up returning the phone and going back to my traditional plan. ATT has lots of quirks - no international SMS (pathetic!), inflexible policies, and no WAP/Web/Data capabilities unless you go the GSM route, which is a pity - but they are a pretty solid bet for voice in the short term. Within a year, 'number portability' may be a reality so one can always switch then!

I do have Cingular also, and even in and around the office in Walnut Creek I see 'emergency only' quite often; not sure why exactly! I don't use it enough to have a strong opinion; I use it primarily to send SMS to Europe, since ATT can't handle that!

Everything written above is my best understanding based on a couple of months intensive research (selecting a personal phone and a corporate phone plan for my company). Please correct/elaborate as you see fit!