The cisco 79XX series of IP hardphones was and is Cisco's mainline of IP hardphone endpoints.
These phones come in several packages from cisco;
(1) 79XX with Call Manager License with SCCP firmware installed from factory
(1) 79XX Spare with Call Manager License with SCCP firmware installed from factory
(1) 79XX without license with SCCP firmware installed from factory
(1) 79XX Spare without license with SCCP firmware installed from factory
There's little to no one here at 3CX that runs Cisco IP PBXs (i.e. Call Manager & Call Manager Express), except me and Mike Harris. So do not purchase a Cisco endpoint with a Call Manager License.
As previously stated most if not all IP phones DIRECT from Cisco come preloaded with Cisco SCCP firmware. SOME, but not all, Cisco 79XX series IP hardphones support multiple protocols such as SCCP, SIP and MGCP. SCCP is Cisco's VoIP standard, SIP is the industry standard and MGCP is a telecommunications standard of sorts.
To correctly process a transition between a cisco IP hardphone from SCCP (most common base installed firmware) to SIP firmware following the flow below;
(a) determine your make and mode of cisco IP hardphone. Determine it's SIP functionality via cisco's site, voipinfo.com or even ebay. What your looking for is 'Supported Protocols'. It should indicate 'SIP'.
(b) determine your firmware currently installed in your cisco IP hardphone. This step is often overlooked but important. Because there is a cross-matrix of what SCCP to SIP conversion is available. Meaning, if you have a OLD SCCP build, you cannot upgrade directly to the latest SIP firmware from cisco. You will have to upgrade to a OLD SIP firmware first and basically upgrade 2,3,4 times until you get the correct STABLE, TESTED, and SUPPORED SIP firmware your project requires. Notice, I did not say the LATEST firmware... often the latest SIP firmware is not stable, nor supported, nor recommended for usage in production environments.
More information here:
http://www.cisco.com/en/US/products/hw/phones/ps379/products_tech_note09186a0080094584.shtml
(c) Once you have determined your software information you need to locate valid cisco SIP firmware files. Notice I say FILES not not IMAGE or FILE. There are multiple files required for SIP conversion and SIP operation. Cisco SIP firmware can be located in various fashions, if you have a SMARTNET agreement like I do, you log in and download the software you need. But if you don't then its more complicated. Cisco, in their infinite wisdom has restricted most software downloads to only registered cisco users with ATTACHED SMARTNET agreements.
Surprisingly the best way to locate the SIP you require is simply registering on cisco, so the download links allow you to select IP phone firmware, and you will get to the last screen showing the SIP file you need. You will not be able to download the files because you do not have a SMARTNET agreement BUT... you will see the file name 'P0S-8-2-XXX (whatever). Now cut and paste that exact filename into your google or yahoo. Some people out in cyberspace have uploaded their cisco SIP files to webservers. When you hit 'search' you should get several pages of websites with these files. Download them and your one step closer!
(d) Basically... at this point because I could end up writing a 30 page instruction book....here is the short version
(e) setup isolated PC with PUMPKIN TFTP server
(f) put your cisco SIP files in the TFTP directory
(g) boot up your cisco IP hardphone
(h) point your cisco IP hardphone to your IP address of your PC with PUMKPIN TFTP
now... with a 7941G or 79XX series with a LCD screen this would be as easy as navigating to the setting screen and select TFTP server and inputting your TFTP server IP address. But since your phone does not have a LCD you will have to use a wire-sniffer application like wireshark (wireshark.org). You will need to 'sniff' out what TFTP server IP address your phone is trying to locate. When you boot your phone up it will 'seek' out it's programmed TFTP server. Because you cannot use it's LCD screen (because it does not have one) you will need to 'sniff' out what IP is programmed into it from the previous owner or factory configuration. Once you find out it's IP and the IP it thinks is it's TFTP server... change your PC running PUMPKIN to that TFTP server IP address. That way... when your ip phone boots up.. it hits your PC and PUMPKIN requesting the firmware it needs to be upgraded.
(i) upgrade the phone with the matrix compatible SIP firmware... then upgrade again into the next tier of SIP firmware...for instance SCCP OLD should be upgraded to SIP POS2XXX, then SIP POS3XXX, SIP POS4XXX. While some people would recommend going more... I have had better luck upgrading in smaller steps. Remember, WHEN YOU HIT SIP version 7 YOU CANNOT REVERT BACK TO a lower version of SIP.
So as you can see... SIP on cisco phone... well, not fun. I would rather listen to my wife tell me how loud my cisco routers and switches are. Basically cisco wants you to use their IP phones on their solutions (i.e. CM, CME) and they want you using their protocol SCCP. So in turn they have made the SIP conversion process... well, sucky. Plus, once you convert cisco IP phones to SIP... they lose their webpage configuration ability. Plus, people have reported SIP converted phones freeze and have static in audio and do not operate as well as other SIP hardphones.
Your solution is easy. For $30 - $50 grab a SNOM (mike your laughing I know cause you love these ugly little buddies) or Linksys SPA, or Polycom (which are nice but pain in the butt to setup as well).