"SIP is the most popular VoIP protocol. This protocol
enables two or more people to make phone calls to each other using
the Internet to carry the call. SIP to SIP calls on a broadband
internet connection are high quality, always free regardless of
distance, and offer additional functionality such as free voicemail
to email and phone numbers, caller ID, 3-way conference, speed
dialing, call forwarding, simultaneous ring, call waiting, call
return, caller ID block, and anonymous call rejection.
"Softphones are user based clients for making and receiving
voice and video communication over the IP network, usually
permitting integration with USB and IP Phones instead of a
computer's microphone and speakers (or headset). This article
selects the best softphones available for Linux.
"We have included Skype in the list. Whilst the Skype client is
available for no-charge, it runs on a closed proprietary network,
and is therefore not 'free' software. However, given the importance
of Skype in promoting VoIP, we believe it warrants a place.
"For enterprise or business markets, VoIP enables the enterprise
to manage a single network (the IP network) instead of separate
voice and data networks, while enabling advanced and flexible
capabilities to the end user. With the credit crunch still to take
full effect, it's even more important for small businesses to
minimise their costs. One way to reduce expenditure is to switch
from a normal telephone contract to using VoIP. Calls made using
VoIP work and sound like normal telephone calls, but cost
significantly less. Public Branch Exchange (PBX) is a private
telephone exchange which routes calls internally and provides call
queuing, hunt groups, conference calling, voicemail and more. The
PBX enables many phones to use a single VoIP connection."
