An IP Phone resembles an ordinary POTS phone but is connected to the external world via an Ethernet network cable (normally Cat5) rather than a Telecoms cable. It may well have a dedicated telephone number and/or an extension number but it must have a Network Address. Voice traffic enters and leaves the phone in internet data packets, and call set up and control is all achieved over the internet.
IP Phones are available from hundreds of manufacturers, although many of these are based on the same two chip sets. They vary in many ways, the most obvious being price. Quality of keyboards, cabling, microphones, speakers and packaging is part of the reason with effects on ease of use and service life.
Specification or functionality variation across this range is striking. Physically this is manifested in the number of dedicated function keys and the size of any display screen. Some expensive IP phones have video phone capability. Many are speaker phones where the user can choose to use a built in speaker and microphone or the normal receiver. A common feature in mid range phones is the use of "soft keys" where the function of parts of the keyboard changes with context, normally signalled by text on a display screen.
Two cabling aspects are important. Some IP phones incorporate a 2 port ethernet switch so that the phone can be deployed "in line", as it were, to an existing PC on the office LAN thereby obviating the need for additional network cabling or switches. Most phones are powered via a mains adaptor, but some have PoE (Power over Ethernet) capability so that they can be supplied from a PoE capable switch.
Less apparent differences lurk inside the box. Leaving aside IP phones that are designed to work only with proprietary systems, not all phones fully support the relevant international standards, and this can be troublesome if some of the more advanced features of IP telephony are required. For general use, the phone should work behind all the common types of NAT - but some do not.
The interesting internal differences are concerned with what additional functions are built in to the phone. These are over and above what the phone can derive from whatever PBX it may be connected to. Typically they will include Call history, speed dials, last number redials, and phone books.
All the above discussion relates to hardware IP Phones. There is another class of IP phone called Soft Phones. These are software packages that are installed in a computer and which use the computer keyboard, monitor, microphone and speaker for user interaction.
We have extensive experience of IP phone hardware and are always happy to advise when it comes to making your selection.