Cisco Unified IP Phone 7912G – SIP to SCCP
As stated in my last post, I received my CCNP Lab Kit in the post last week.
In my excitement, I decided to switch my IP Phones from the SCCP firmware (which was the software originally on the phones) to the SIP firmware so that I could connect to VoIPTalk.
Now that the excitement has died down a little, I wanted to switch back to SCCP as, from what I can tell, it provides more features than SIP.
As I’m not too familiar with Cisco IP Phones, I started Googling for instructions on how to switch back, but I couldn’t really find any instructions on how to do so.
In the end I tried the same way I had originally upgraded to the SIP firmware. I edited my gkdefault.txt which originally contained the following line:
upgradecode:3,0x601,0x0400,0x0100,0.0.0.0,69,0x060111a,CP7912080000SIP060111A.sbin
And replaced it with:
upgradecode:3,0x601,0x0400,0x0100,0.0.0.0,69,0x070409a,CP7912080003SCCP070409A.sbin
You can read what the values mean on the Cisco site, but all I had to change was two last values of the line:
0x060111a -> 0x070409a
CP7912080000SIP060111A.sbin -> CP7912080003SCCP070409A.sbin
The first value I had to change was the build ID/date, which is (from what I can tell) the last few characters in the file name after the “SIP” or “SCCP” bit.
The second value is pretty self explanatory, its just the file name of the firmware file you have.
Next, I used cfgfmt to convert the file into a .cfg file compatible with the phones, and put it on my TFTP server.
I then restarted the phones, and behold! They were downloading the SCCP firmware image. 
I’m not sure if this is the “correct” way to switch back to the SCCP firmware, but it worked for me and I don’t see why it wouldn’t be correct, it seems pretty obvious. The only reason I am a little confused is the fact that while searching for instructions to switch back, I found a lot of people having difficulties switching back and even some companies offering a “recovery” service for people in this situation.
Hopefully my post will help other people who are in this situation.
Now I just need to figure out how to get the CTU ringtone onto the phone. 
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