Here are a few articles we've prepared on technical topics which other people may find helpful.
The Cisco 7940 and 7960 series IP telephones are great devices for your custom IP telephony projects. Apart from the Cisco-supplied software, these phones work great with SIP servers such as your own Asterisk server, or a VoIP provider who uses SIP-compatible systems on their end.
After working with these phones for a bit, and reading everything I could get my hands on from the web, I learned some of the following advice which will hopefully save you some time during your projects.
Chances are that when you first receive your Cisco phone, you will want to upgrade the firmware version onboard. One main reason to update the firmware is to convert the phone to use the SIP protocol, rather than the firmware for the SCCP protocol it may already be using.
Depending on which version of firmware is already installed on your phone, this will affect the procedure you will need to follow to upgrade or switch your phone's firmware image. There are many procedures described on the web for performing firmware updates, and several of them are correct -- it all just depends on what firmware version you are starting from.
Once the device has been given an IP address on your LAN, you can proceed with configuring it to download firmware updates from a TFTP server. I didn't have a TFTP server already on my LAN here, so I easily installed one on a spare Windows box. A search on Google found a quick and simple solution available as "TFTP Server for Windows". You can download and install this application free for a thirty day trial, which should be more than enough time to upgrade your device. (You could alternately install a tftp server on a spare Linux or BSD computer, but we happened to have a spare Windows workstation here so we used that.)
When the TFTP server program is set up (which takes all of thirty seconds), you simply grab the current firmware from Cisco's website. You unzip the archive they provide, and place the files in the root folder used by the TFTP server software. When the Cisco phone boots up and goes to your TFTP server to find firmware upgrades, it checks for files there to guide the firmware upgrade process and configure the phone. You can use this to your advantage by watching the logs for the TFTP server, and seeing which files the phone is asking for. Once you have this list of files it is expecting, whether they are there already or not, you can proceed to put the proper files in place and get the upgrade under way.
For whatever reason, I was having some problems with these phones losing registration with my Asterisk servers. They simply wouldn't ring when incoming calls should have been coming their way, but outgoing calls still worked fine. One thing I did that seemed to resolve this problem was change the default "Register Expires" value for the phone. You can find this setting under :
The default value on my phones was set to 3600. I changed this to 300, and subsequently, I have not had any problems since then with the phones losing registration. This is especially important for phones behind a NAT gateway (eg a unix machine routing packets, or a commercial cable/dsl router box).