Telephones and cellular phones convert voice or other sound signals into a form that can be transmitted to another device that receives and reconverts the waves back into sound. Telephones can be corded or cordless and use analog or digital technologies. Cell phones are cordless, usually digital devices that are specified as dual-band or tri-band to indicate the combination of supported technologies and frequency bands. Corded telephones consist of a speaker, microphone, duplex coil, ringer, hook switch, touch-tone keypad and frequency generator. Cordless telephones consist of a base and handset. The base attaches to the phone jack through a standard telephone wire and converts electrical signals into FM radio signals. Cordless telephones offer many of the same features as corded telephones, but allow the user to move around freely. Specifications for cordless telephones include model, type, lines of text, recording time, handset talk time, handset standby time, and messaging functions.
Providers of telephones and cellular phones may buy or lease rent a variety of new and used equipment. Mobile telephones and cellular phones use several different technologies. Corded phones and older, analog cellular phones use advanced mobile phone service (AMPS), a 1G standard which operates in the 800 to 900 MHz frequency band. Digital technologies for mobile telephones and cell phones include CDMA, TDMA, GSM, and DECT. Code division multiple access (CDMA) is a digital wireless telephony standard that allows multiple frequencies to be used simultaneously. Time division multiple access (TDMA) is similar to CDMA, but splits the frequency band into a number of channels which are stacked into short-time units. Global system for mobile communications (GSM) is a popular European mobile telephony technology. Digital enhanced cordless telecommunications (DECT) uses smaller, lower-powered base stations than other cellular systems. DECT was designed to replace analog cordless phones, but is now used with many private branch exchange (PBX), wireless local loop, and dual mode GSM/DECT systems.
There are many different types of mobile telephones and cellular phones. Cellular phone specification include form factor, model, frequency modes, memory, weight, dimensions, battery type, battery life, operating system (OS), air time, talk time, phone book capacity, and display type. Some cell phones provide email, games, music, and polyphonic ring tones. Mobile telephones and cell phones with a digital camera, Web browser, and speakerphone are also available. Personal digital assistant (PDA) or PDA phones include either a Symbian® (Symbian Ltd.), Pocket PC or Palm® computer (Palm Computing). These mobile phones are larger and more expensive than other types of cellular phones, but can be equipped with a variety of software. Clamshell or flip-style phones protect a cell phone’s keypad from damage and are usually smaller than other types of mobile phones. Razor phones feature a clamshell-style design, but have an extremely thin profile.