Apple iPhone 4S vs Apple iPhone 4 vs Apple iPhone 3GS

Form factor - Refers to the form factor of a phone. The main handset designs are bar, clamshell, slide, swivel

Side Keys - Buttons on the side of the phone, designed to be used by fingertips while holding the phone - one-handed operation.

Pixel density - The pixel density of a display represents the number of pixels over an area of one inch. It’s measured in “pixels per inch”, or ppi. The higher the number, the more detailed and good-looking the display is.

Technology - There are two main screen technologies currently used in phones and tablets: LCD and AMOLED. The former usually features a light source and liquid crystals, while the latter is based on organic light-emitting diodes. Newer LCD variations like IPS-LCD and Super-LCD allow for very accurate color reproduction and very wide viewing angles, where no significant image quality loss is observed. Current AMOLED screens differ in such a way that they can exhibit much more saturated colors (sometimes too much) and incredibly high contrast levels, which is due to black color being completely black in AMOLED displays.

Colors - Shows the number of colors that the display supports

Talk time - Maximum talk time in hours

System chip - Most modern handsets use an advanced chip that includes many of the device’s hardware modules like the processor, Wi-Fi, Bluetooth and sometimes even the wireless radio. This field shows what particular system chip (or System-on-a-Chip) is used in the phone.

Processor - The processor is the main computing component of a phone and is a major factor when it comes to the overall speed of the device. Some more powerful smartphones use dual-core and quad-core processors designed to deliver greater performance.

System memory - System memory, or RAM memory is the type of memory that the device uses to temporarily store data from the OS or currently-running apps. The more RAM available to the device, the better the performance will be when multiple or heavier programs are running.

Video playback - Video support such as MPEG4

CDMA - Code Division Multiple Access. A technique of multiplexing, also called spread spectrum, in which analog signals are converted into digital form for transmission. For each communication channel, the signals are encoded in a sequence known to the transmitter and the receiver for that channel. The foremost application is digital cellular phone technology from QUALCOMM that operates in the 800MHz band and 1.9GHz PCS band. CDMA phones are noted for their excellent call quality and long battery life.

GSM - Global System for Mobile communications. A world standard for digital cellular communications using narrowband TDMA (Time Division Multiple Access), which allows up to eight calls at a time on 800 MHz and 1800 MHz frequencies. Introduced in 1991. Is the standard most commonly used in Europe and Asia, but not in the United States. GSM phones use a Subscriber Identity Module (SIM) smart card that contains user account information. Any GSM phone becomes immediately programmed after plugging in the SIM card, thus allowing GSM phones to be easily rented or borrowed.

UMTS - Universal Mobile Telecommunications Service, also called WCDMA, is a 3G (Third Generation) packet-based transmission of text, digitized voice, video, and multimedia at data rates up to 2 Mbps. It is based on GSM standard and is supported by major standards bodies and manufacturers

Data - Shows the particular phone's type of data. the major mobile phone data types are GPRS, CDMA2000 1xRTT, EDGE, CDMA2000 1xEV-DO, UMTS, etc.

Global Roaming - Global Roaming is the convenience of having a mobile phone to make and receive calls, send and receive SMS while you travel overseas with your regular mobile number. Usually the Global phones support multiple frequencies like - 900/1800/1900 mhz.

Positioning - This field shows the positioning systems supported by the device. There are three main types: GPS, A-GPS and GLONASS. GPS - This is one of the most widespread global positioning technologies, developed and maintained by the U.S. government. It uses satellites in order to detect your location. Works best in clear weather. A-GPS - A-GPS stands for Assisted GPS and is the industry standard for positioning and navigation. “Assisted” means that it can use local wireless networks, in addition to satellites, for quicker and more precise localization. GLONASS - GLONASS is a global positioning system, developed by the Russian Federation. It’s very similar to GPS, but isn’t so popular in cell phones.

Wi-Fi - Wireless Local Area Network (WLAN) - used radio waves (RF) or infrared signals to send and receive data over the air. Most popular WLAN solutions today is Wi-Fi (802.11b and 802.11g) standards. 801.11b provides data speeds of around 11mbps while 802.11g can go up to 54 mbps.

FCC approval - The Federal Communications Commission (FCC) is an independent United States government agency, directly responsible to Congress. The FCC was established by the Communications Act of 1934 and is charged with regulating interstate and international communications by radio, television, wire, satellite and cable. The FCC's jurisdiction covers the 50 states, the District of Columbia, and U.S. possessions. Every wireless phone device that that is sold in the U.S. has to be tested and approved for sale by the FCC.

FCC measured SAR - The exposure standard for mobile devices employs a unit of measurement known as the Specific Absorption Rate, or SAR. The SAR limit stated in the international guidelines is 2.0 W/ kg*. Tests for SAR are conducted using standard operating positions with the device transmitting at its highest certified power level in all tested frequency bands. Although the SAR is determined at the highest certified power level, the actual SAR of the device while operating can be well below the maximum value.