Originally Posted by mdriftmeyer
Doesn't it feel that talking to these profiles [specifically about this subject] is right up there with talking to first graders?
And most don't have a good understanding of the basic technologies to appreciate the complexities involved.
Perhaps the following excerpt will help. It may ned some further vetting and updating, but it is one of the best descriptions on wireless protocols we have seen."GSM and CDMA are different wireless protocols, or "air interfaces".
GSM is a worldwide nonproprietary standard. It is a variation of TDMA - time division multiple access. It allows many phones to use the same radio channel via a technique of "time slicing": each phone on the channel transmits only during its allotted time slot.
CDMA is a proprietary standard and while there are CDMA systems in over 50 countries, it is not the "world standard" - if you want a "world phone" you want a GSM quad-band phone. South Korea is one of CDMA's chief users besides the US. CDMA stands for "code division multiple access." It uses a spread-spectrum technique; different phones share the same channel by using different spread-spectrum keys.
On top of these differences you have to consider frequencies. GSM in North America uses two bands, 850 MHz and 1900 MHz. GSM in almost all of the rest of the world (ROW) uses two other bands, 900 and 1800 MHz.
These days most any GSM phone you get will be at least a dual-band phone: it will work on both bands used in your area. If you plan on traveling internationally and you want to use your phone, you can get tri-band GSM phones that work on both US bands and one of the ROW bands. Or if you live elsewhere you can get tri-band GSM phones that cover both of the ROW bands and one of the US bands. And of course there are quad-band GSM phones that cover all four. These will work on *almost* any GSM system in the world, assuming you have either a local SIM card or that international roaming is turned on for your account. There are a few oddball systems out there on different frequencies entirely.
CDMA has similar issues with frequencies. The first big build of CDMA in the US was by Sprint; they used 1900 MHz exclusively and called it "PCS". Verizon's CDMA towers use the same CDMA protocol, but on the 800 MHz band.
Most CDMA phones sold in the US will work on both bands so that you can roam on the other carrier's towers. In fact a lot of Verizon's older phones were "dual-band/tri mode", meaning they would work on both of the CDMA bands and also on the old AMPS analog towers (also 800 MHz). The need for those has gone away since many of the old analog cellular systems have been shut down. Sprint's PCS phones were orginally 1900 only, but most of their phones now are dual-band CDMA.
CDMA in South Korea uses different frequencies entirely; no US CDMA phone will work there, nor vice versa, even though we both use CDMA. (n.b.: If you travel to South Korea, there are phone rental booths in the airport... or at least there were the last time I was there. You can even keep your same number on the rental phone.)
There are CDMA systems in other countries here and there but in almost everyplace other than North America and South Korea, GSM is dominant.
So, so far we have GSM phones that might be dual-band (either North America or ROW only, not both), tri-band, or quad-band; and we have US CDMA phones that work on the two US CDMA bands; and we have South Korea's CDMA phones that work in South Korea. Of course GSM phones won't work on any CDMA tower, nor vice versa.
None of these provide 3G capabilities.
3G is not a specific air interface protocol. It is more of a name for a set of features and capabilities - if your system meets a specified set of capabilities (like data speed, simultaneous voice and data from the same phone at the same time, many others), you can call it a "3G" system. Just like both CDMA and GSM are commonly recognized as 2G or 2.5G (depending on features like EDGE), there are several different air interfaces that are all called "3G" and provide 3G capabilities. Yes, one of the key 3G capabilities is data transfer speed for a data connection - but there's a lot more to it than just higher data speed. The WIkipedia article on 3G has the details.
There are two 3G systems in common use today. One is called EV-DO. This is an extension of CDMA and accordingly is commonly found as the 3G upgrade to existing CDMA systems. So the 3G offered by Verizon and Sprint in the US is using EV-DO.
The other 3G system in common use is called UMTS. It is designed as the 3G upgrade for existing GSM providers.
There are frequency issues here too, just as there are for CDMA and GSM.
Both AT&T and T-mobile are providing UMTS.. but on different bands. My HTC TyTN II does quad-band GSM but it will not work on T-mobile's UMTS (1700/2100 MHz). It does work on AT&T's UMTS (850/1900 MHz), and also on UMTS in Europe (2100 MHz, but different from T-mo's 1700/2100).
UMTS includes an optional upgrade called HSPA. One piece of that is called HSPDA, which provides what is being called 3.5G data speed.
Note that 3G is not just for data access. 3G systems provide both voice and data services. My HTC phone will not work on any 2G system in Japan. However, it does work on Japan's UMTS systems (2100 MHz). Thus my phone works for both voice and high speed data in Japan, relying solely on its 3G capabilities.
Now... that covers the differences between the systems, sort of. There's a lot more detail and I've simplified a lot, but those are the basics.
Can you have a phone that has GSM, CDMA, and 3G? Yes - the Blackberry Storm is one example. It does CDMA in the US; it does quad-band GSM for near-worldwide GSM service. It does both EVDO (3G in the US) and UMTS (3G 2100) in many other countries.
Yes, it is standard GSM. I was surprised that they did quad-band GSM; I thought it would be ROW GSM only, but it is indeed quad-band. However it will usually not work on GSM in the US because there will usually be a Verizon or even Sprint CDMA tower handy; Sprint and Verizon have roaming agreements with each other such that using each others' towers is transparent and doesn't usually incur "roaming" charges even if the phone says you are roaming. About the only "non-USA" thing about it is that it won't do UMTS on any US carrier, but this doesn't make it not true GSM.
Also note that even if there were no CDMA/GPS/3G phones on the market, this would not prove that it isn't possible. It would only mean that no one has done it... this is usually for economic reasons. Carriers love to lock you into their systems and keep you there, and making your phone work on as few other systems as possible is one way they do that. The only reason Verizon and Blackberry decided to make the Storm is that Verizon was tired of losing world-traveling customers (who wanted a single phone they could use worldwide) to AT&T and T-mobile. It used to be if you wanted a "world phone" (or as close as is possible given the hodgepodge of "standards" around the world) you had to go to one of those carruers and get a quad-band GSM phone; no more." Sullivan. http://in.answers.yahoo.com/question...2042019AAt9J2P