Flash a Cisco 7940 Phone to SIP Firmware

Just thought I’d post this here to share my experience of the process upgrading these phones’ firmware in hopes that it might be useful to someone / anyone.

First, download the SIP firmware from this website: http://downloads.3cx.com/downloads/misc/CiscoOS79XXSIP.zip

Or a similar one from Cisco’s site (some may be unavailable if you don’t have a service contract or something with Cisco, but don’t despair… chances are you’ll definitely be able to find a copy of what you’re looking for somewhere on the internet).

Set the TFTP IP address and file name ( os79xx.txt ) on your firewall / router (pfsense?)

This TFTP IP address should point towards a linux or other server with a TFTP server running, and in the root folder place all the files that you downloaded.  Customize SIPDefault.cnf / XMLDefault.cnf.xml with stuff that will go on ALL the phones that you’re flashing.  For configurations to go on only one phone, use SIP(macaddress).cnf or whatever.  To find this out, start up your cisco phone.  Press the settings key to find out the MAC Address.  Note this and then use it to make files for use on only unique phones.

P0S3-8-12-00.sb2 is the firmware I used.  Make sure to use P0S3 (sip firmware) instead of P003 (non-sip firmware).

Once your firmware is in the root directory of the TFTP server and you’ve got everything all set (in os79xx.txt make sure it says the correct SIP firmware version to flash) then…

Power Cycle the phone and clear the configuration by holding down the # key and then plugging in the phone. After all the lights cycle on the phone, release the # key and press 123456789*0# followed with the 2 key (to clear all the network settings).

After you’ve flashed the phone sometimes to get your configuration to stick you’ll need to power cycle the phone.  To skip the step where your phone waits on “VLAN Configuration”, hold down the pound key on boot, and after the lights cycle hit 2 or another key to speed up boot a bit.

Useful links:



To monitor what’s going on with the TFTP server, enter this command:

sudo tail -f /var/log/messages | grep in.tftpd

Once you have the phone up and running, and it says UNPROVISIONED SIP at the top, hit the settings button, go down to Network Configuration to verify settings:

  • Make sure DHCP Server has the correct IP / gateway set
  • Check Default Router
  • Check DNS Server

All this stuff should be automatically set by your DHCP server but you never know!! So check.

Proceed to go back to Settings, then head down to Unlock Config.  Press Select and then try the default password of “cisco”.  If that isn’t the password refer to your documentation. If you want to have wireless internet in your home then I recommend for you to check out best routers from https://reviewsfield.com/best-wireless-routers/

Then head up to SIP Configuration.  This is where the fun begins!

  • Enter Line 1 Settings and edit Name.  Enter your SIP username.
  • Enter a short memorable name for the account into Shortname.
  • Enter your SIP username again into Authentication Name.
  • Enter your password into Auth. Password.
  • Enter a memorable display name for the account into Display Name.
  • Etc

Head back from Line 1 Settings to the main SIP Configuration menu.  Then:

  • Scroll down to Preferred Codec – it should be g711ulaw, but if not, switch it to that one.
  • Change Register with Proxy to YES
  • Change Register Expires to 180
  • Enter a backup proxy or an emergency proxy if you’d like (alternate servers on VOIP.MS)!
  • Outbound proxy is unnecessary for VOIP.MS
  • Make sure that NAT Enabled to NO
  • Edit NAT Address and set it to your default gateway as you saw above in network config

To enable a logo, refer to this page:


As far as the logo is concerned, I have been running into an issue with an HTTP connections, I need to try a local server as opposed to one over the internet, perhaps that will solve the issue?

Let me know how your VOIP setup went!!!  Thanks for reading.

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Categorized: How Tos
  • Sergio

    Thank you for the information!, I hope it works.. I´m deciding if I buy a CISCO 7940 phone to configure with my SIP… if I do, I´ll come back and tell you how it went.. thanks.

  • http://www.mydailytech.com/ Connor McBrine-Ellis

    Cool! I recommend them. They are great. Built like a tank as well.


    Hey – Connor. I desperately want the WMP 11 downgrade for 7, but the file has been taken down. Could you somehow get it to me via e-mail or whatever? Pretty please …?

  • http://www.mydailytech.com/ Connor McBrine-Ellis

    Hi friend, I’m really sorry – this probably isn’t the answer you’re looking for, but I don’t really have those files anymore & that is a *REALLY* old post. Why not give a player like foobar2000 a try?


    Hi, good to get in touch! However … I know, but oh no?:/ Well … I like my stuff a certain way and am not much for unnecessary change if I can avoid it somehow. WMP 11 has the look and features I want & need, simply. Thanks for the tip though. If you ever get the chance to get over the files again … you know who’d be really happy.