This section intends to capture the state of the art in IP systems as this book goes to press. It is not an exhaustive catalog of available products, merely examples that represent capabilities and feature sets. Inclusion doesn't indicate an endorsement, and not appearing here means only that a product isn't listed here. When preparing to select a system, you may want to consult various comparisons of telephone systems like the Sourcebook of Hosted and Cloud-Based VoIP and Unified Communications Services at webtorials.com.


IP phones from 10 years ago look inadequate today. Many early models were discontinued and replaced in a year or two because they lacked the CPU cycles, RAM, and interface controls to support all the emerging features buyers wanted.

The new models should last longer. They have many more buttons, larger displays, more powerful CPUs, enhanced software, and they conform to many of the standards and RFCs published in the last five years. The pace of developing new phone features in SIP continues steadily, but most of the essentials are now offered widely.

Few IP phone yet support IPv6, though that feature has appeared. With some planning, IPv4 phones will adapt to v6 with a software update. Because their RAM or CPU may not be sufficient to run a double protocol stack of both IP versions, a phone operate only one at a time.

A primary differentiator of a phone is the number of line appearances it can handle. On the ...

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