Hi
Thank you all for this thread. I recently bought some mitel 5312 phones and couldn't get anywhere. By following the instructions on this thread and downloaded the firmware I got all the phones working on a FreePBX. I think the original firmware was 5.x.x.x don't remember the actual number. I could switch them over to sip mode but when I tried to access the web page it asked for a language file. Tried a few tricks but nothing worked.
So Thank You again,
God bless.
mosa