Advice on Mobile Technology - What mobile phones will work for me?  What are Quad- Tri- and Dual-band phones?  What are Data Services?

Carrier Specific vs. Unlocked Mobile Phones

Many mobile phones (and PDA and smartphone devices) which are for sale on eBay are phones which were purchased through North American carriers.  The largest North American Carriers are AT&T, T-Mobile, Verizon, Sprint Nextel, and Rogers wireless (Canada).  In NA, these carriers work with the handset manufacturers to "lock" the devices so that they only work on each specific carrier network.  This practice of restricting the phone provides some security to the carriers, and they sell the phones at a subsidized price to the consumers figuring they make more money by locking consumers into long service contracts.

A "locked" device normally will only work on it's original network, so AT&T phones will only work on the AT&T networks for example.  However, some devices can work on other carrier networks - all you have to do is call the carrier that you want and ask them to run the ESN - the Electronic Serial Number - found on the back of every phone, normally under the battery.  This number is transmitted every time you make a phone call, it's how the carriers know who you are and how to bill you.  Any carrier can tell you, before you purchase the phone on eBay, if you'll be able to use the phone on their network.

Some phones will actually work on multiple networks.  These phones have been reprogrammed and are referred to "unlocked" phones.  They are normally more expensive because they can be used without a service plan and are portable between the different carriers.  Many of the phones available in Europe are unlocked - in fact, in most of Europe you purchase a phone and service from different companies.  In the EU, a phone is just another electronic device - like a TV, and the phone service is just another utility, like a cable television subscription.  Funnier still, in some European countries you purchase televisions which are subsidized because of long-term cable or satellite television subscriptions.

Finally, and to add to the confusion, some locked phones can be used on different carrier networks.  I've popped in SIM cards into "locked" devices and seen them work forever on an alternate carrier, and some work for 24 hours and then can't register any longer.  The only real way to tell is to ask the carrier to check on the ESN.

Dual-band and Tri-band and Quad-band phones

The GSM networks in North America are different from the ones in Europe.  Most of the world uses GSM-900 and GSM-1800, while the North America and most South American countries use GSM-850 and GSM-1900.  These numbers refer to the radio frequency in megahertz that the devices transmit on.  So, your fancy-pants new GSM phone that you just bought on eBay may not work in Europe or even on vacation in the Carribean, even though it's a GSM phone!

Dual-band phones work with the two GSM standards in one geographic area - for instance GSM-900 and GSM-1800 in the United States.  Tri-band phones work with the major two standards, and the most widely supported standard elsewhere - for example, a Europian tri-band might support GSM-850 and GSM-1900 in Europe, and GSM-850 in the US.  A Quad-band phone will support all 4 major standards.

Don't confuse GSM or the global standard for mobile communication with GPS or the global positioning system - they are unrelated.

Data Services

Most phones these days provide access to data services.  Every carrier calls the plans something different because some marketing department decided that a flashy name might entice more customers.  If you need data services, you should go for the unlimited data plan and it should cost somewhere around $20 per month in the US.  If you don't know if you need data services, then you don't need them - just leave it at that.  Now that people are using data services more heavily on devices like Blackberrys and iPhones, carriers are increasing pricing for their same old data services that older mobile phones use.  I expect that to even out over time, after all you don't pay more for using more internet on your cable or DSL line - although in the mid-90's you sure did.  One of the carriers will re-introduce unlimited data for $20 and everyone else will follow.

Different phones support many different types of data connectivity.  Some let you browse the whole real internet from your phone, some just give you access to a small sub-set of pages that the carrier provides, which normally include sports, news, weather, maybe some shopping.  Some of these interfaces are called WAP pages, which is just a text-based web browser - actually it's older technology that was supposed to keep us occupied until the networks could support full speed data services, but it's still widely in use today.  Some support WiFi or 802.11(b)(g) and soon to be (n) - that's the same wifi or wireless internet connection that you use at starbucks on your laptop.  Handy for travel when you don't want to lug around a laptop for basic browsing.

Some phones have a modem built in - this means you can use your mobile phone as a modem with your laptop computer, normally either through a cable, an infrared port, or a bluetooth connection.  Don't expect broadband speeds, they are more like slower dial-up speeds - and if you roam outside of the GSM network, which is still largely centered around major cities and highways, you'll drop your data services and loose connection altogether.

Still some other phones just allow you to sync your data with your PC - so your contacts and appointments and notes and tasks all stay up to date.  While they are called data services, they are free, and just require the time and patience to install applications from the phone manufacturer on your PC.  Once you get through that, you can download MP3s to your phone, grab phone cam pics and email them from your PC for free (no MMC message charge for me, thanks), you can even install java applications and games to many devices - they are available online and are normally completely free.

There are different network services too.  New services are called 3G for third generation.  They include HSDPA and WiMax networks.  2.5G networks like GPRS, the General Packet Radio Service.  It works over GSM, and you can talk and use data services at the same time.  GPRS can be compressed with a protocol called EDGE, which allows for about 3 times greater than the GPRS data transfer rate over the GSM network.  EVDO is another data service technology which will allow for broadband-like speeds.  Check with your preferred carrier to see which data services they offer, and also remember to check for the network coverage maps of those data services, they may not be the same as your voice coverage maps.

Closing thoughts...

Consider the long term costs of your mobile phone before deciding to break a contract and sign up for 2 years with a few hundred dollar per month committment.  I have a very old and inexpensive voice plan from my carrier and I plan to keep it as long as possible.  As far as data services are concerned, aren't you in front of a computer enough every day?  I know that I am.  If you are constantly out and about and traveling frequently, maybe $45 a month for full mobile data services is worth it for you, or maybe you can get away with a device that has a wifi radio so you can use wireless hotspots for free.  Buy the device and the services that you'll actually be able to use, and be honest with yourself about what you need and what is worth paying for.

Happy Shopping!