Cisco Telephones - Protocols.

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At any time there are plenty of Cisco phones being offered for sale on ebay. Unfortunately the sellers vary from super-knowledgeable, to knowing nothing about what they have other than reading the part number from the back. There is no doubt these phones are very nice pieces of kit, a world away from the VOIP phones coming in from the far-east.
Almost all the phones you see for sale as used have been previously used in offices, probably well used, but they can take it. Almost all of them will have been used with a Cisco Call Manager exchange. If you intend to use one with other Cisco hardware stop reading now - this guide is not for you.
Most used Cisco phones come with a VOIP protocol called SCCP (skinny as it is sometimes called). With new phones you should have a choice - ask. SCCP works great with other Cisco hardware, is just about supported with Asterisk (an open source exchange), but for other VOIP providers - forget it. Far more useful is the SIP protocol, highly supported on Asterisk and can be used by all those VOIP providers offering cheap international calls. (By the way forget about Skype, that is another world of hurt).
Some sellers, who know what they are doing, will have already changed the firmware to support SIP, or will do it if you ask. However some Cisco phones cannot be changed to SIP - the firmware doesn't exist. If you want to change the firmware yourself, be prepared for a steep learning curve. You will need to be confident using a DHCP and TFTP server - if that last bit didn't make any sense - give up now. If it did make sense Google is your friend, all the information is out there.

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