well then what about AT&Ts 3g?

The numbers are particular frequencies - a device radio that can send/receive, say, in the 1700 band, can't pick up the 1900 band, or any other band. IE: A device needs to support those specific bands to be able to pick up whatever internet/connection is available on that band.

The N900 only support the 900, 1700, and 2100 bands for their 3G. AT&T only offers 3G on the above bands (850/1900). This is done on purpose because if, say, Verizon and AT&T used the same bands, their signals would interfere with each other. So around the world there's different standards which determine what bands will be used by who. Most of the world uses the same bands for G3, but in the US T-Mobile, Verizon, and AT&T get their own bands (Not sure about the other providers). So if a phone's hardware doesn't have the ability to pick up a certain frequency, there's no amount of hacking that can make it do so as far as I know.

P.S. It wasn't the 4 in the iPhone 4 that made me think it had 4G support, I just thought I remembered comparisons between it and Evo 4G, so I think I or whoever I was reading may have misinterpreted the information we got to think it could do 4G.

- Edit - Before anyone misconstrues, I get that signals don't have to necessarily interfere with each other - or else the majority of the world couldn't use the same couple of bands for all of their providers, but I suspect that to do this they had to make phones somehow identify which signal is coming from where. The countries that use the same bands do so because they had the foresight to try to make all phones be compatible with all carriers. The US operators either didn't bother, or just didn't think about it because they were the first providers of average-consumer-affordable mobile phones, and so there hadn't yet been any annoyance from people wanting to switch providers but keep their unlocked phones. Etc. Actually, now that I think about it, I think it might be the exact data-encoding technology that makes it so that, say, T-Mobile can't use the same bands as Verizon.

Honestly, if you want the details, you'd probably have to dig around. Wikipedia would honestly most likely have a detailed explanation of this. The only thing I can say for sure without being wrong or accidentally misleading in some way is just that the N900 can only pick up certain frequencies of signal, and AT&T uses a different set of frequencies.

Actually, You're correct, if they all used the same exact frequencies and channels then there would be a lot of interference and issues with connecting and what not. Similar to how there can be interference between WiFi devices and other 2.4GHz wireless devices such as cordless phones (not cellular) or wireless controllers within the same house on the rare ocasion they are all operating at the same frequency and channel. The frequencies you listed (900, 1700, 850 etc) are "bands". These bands are then split into more specific frequencies for upload (824.0 - 849.0 for the GSM 850 band) and Download (869.0 - 894.0) These specific frequencies are further separated into a wide array of channels. Furthermore, in the USA, carriers have to acquire licenses to use these frequencies in each region from the FCC. For example, when you hear about the FCC "auctioning off" the 700MHz band (or any other), that means they're selling licensing rights for carriers to use specific frequencies and ranges called "blocks" (or in some cases, shoudl the company desire to and bid successfully, the whole band) within a given region.

http://www.3gpp.org/ftp/Specs/html-info/45005.htm
http://en.wikipedia.org/wiki/700_MHz...ectrum_auction
Also, a great grapics showing how various spectrums have been designated: http://upload.wikimedia.org/wikipedi...o_Spectrum.jpg

I'm not sure how things work in Europe in regards to licensing off spectrum, I imagine its a similar process, but the overwhelming reason is the spectrums were designated at different times, and thus inter-regional cooperation and standardization of the spectrums was not a concern. T-Mobile does use the same UMTS bands in the USA as is standard in Europe for the most part (I believe), while AT&T and the others do not.

When more users are active in a cell, its coverage area shrinks. More subscribers and/or more use per subscriber without corresponding infrastructure upgrades means reduced coverage, as well as the (more obvious) issue of congestion on backhaul.

But don't worry, it's negative feedback, so eventually (yay for 2-year contracts! ) people will leave AT&T for other networks and things will approach a steady-state solution. :/