On the page here:
http://www.voip-info.org/wiki/view/Mitel+SIP+FirmwareIt says "In general it is important to upgrade older firmware in sequence - eg: v3 -> V4 -> V5 -> V6 etc. without skipping any releases. Failure to do this (eg: upgrading from V3 directly to V6) may brick the phone."
And the release docs from Mitel for 7.2 say
"If you are running Rel 3 software, you will need to upgrade to Rel 4 prior to going to 5.0.0.21. It is strongly recommended not to upgrade through the GUI. Only the Boot (Set) upgrade should be performed if your are running software lower than 6.0.0.19.
For all SIP Phone types running any software previous to Rel 7.2, this includes Rel 3.0, Rel 3.1, Rel 4.0, Rel 5.0 MUST upgrade to Rel 5.0.0.21 prior to upgrading to Rel 7.2.
Rel 5.0.0.21 is required as a stepping point up to Rel 7.2. Any other method of upgrade could result in corrupted Flash Memory on the SIP Phone resulting in a permanently dead phone."
The first bit of that is red.
Got the release notes, and revisions 4,5,7 from here:
http://dl.dropboxusercontent.com/u/24892334/mitel_firmware.zipNo idea who uploaded that.
But yeah, that's why I'm assuming incremental updates.
Sounds like I can skip 6 though. But no mention of anything previous to 3, when I'm on 1. So I want 2 and 3 at the least, and would prefer 6.