Protocols - (GSM vs TDMA vs PCS vs IDEN vs CDMA vs 3G or 4G/WiMAX)
Each of the major cell providers uses unique protocols and frequencies to connect a wireless device to their network. Different cell providers offer the same protocol support on different frequencies. A Multi-band (frequency) phone will have more options for use with multiple carriers or overseas.
GSM - Cingular (Now AT&T), T-Mobile and AllTel use this standard. So does most of the EU and many other parts of the world. Note: AT&T customers see TDMA info below.
If you have an unlocked (see Locking below) GSM device, you can use it on any other GSM network, simply be replacing the SIM card. This means if you are currently a Cingular customer you can potentially use your newer Cingular phone on say T-Mobile's network.
TDMA - An older analog (vs digital) protocol that is rapidly being replaced by the various digital protocols. Note: AT&T has announced that it will be charging cutomers with older TDMA-based phones a $4.95 p/mnth fee if they don't upgrade their phone.
PCS - Sprints was the first and is still the primary user of this digital protocol. Because of it's shorter range, it has the least coverage of all of the digital protocols. Now that Sprint has merged with Nextel(see IDEN below), the two companies are working towards a common standard. They have just announced a move towards 4G/WiMAX (see 4G/WiMAX below) which will require ALL Sprint/Nextel customers to upgrade their phones over the next couple of years.
IDEN - This is the digital protocol that Nextel and Motorola used to introduce the world to 'Push-to-Talk' cell phones. Since their merger with Sprint, Nextel is moving quickly towards a next-generation 4G/WiMAX infrastructure, with Sprint’s PCS as an interim standard.
CDMA - Verizon uses CDMA technology. They have built out an extensive coverage infrastructure using this protocol. In fact, their 'It's the network' slogan you see in their commercials highlights this fact. Despite the 'hype,' the GSM protocol has 20% greater overall coverage than CDMA. Like Sprint/Nextel, Verizon is looking to move to a 4G/WiMAX standard in the next couple of years.
3G - We will likely never see 3G here in the states. Although 3G systems have been widely deployed in places like India and South Korea, the US market is skipping past 3G in favor of 4G and WiMAX offerings.
4G/WiMAX - The future standards/protocols on the block. Adoption has been announced by Sprint/Nextel, with other carriers looking on closely. The standard for WiMAX is still in flux. It has the potential for allowing a phone to intelligently switch from a WiFi network in your home/office to a cellular provider and back again on a single call.
