I recently found an old LG-Nortel 8540 and decided to put it to my Lync 2010 environment (all other phones are almost all Aastra).
The device had an old OCS 2007 RTM firmware: 1.0.522.101 (1.23). Apparently I am lucky – people with older firmware must to install OCS 2007 RTM in order to update the device firmware to this version (http://www.confusedamused.com/notebook/updating-your-tanjay-firmware-from-10199-123/). 
Issue: My device successfully connected to Lync (with old firmware) but did not want to upgrade it to a recent one – 4.0.7577.410
Resolution:
1. I installed OCS 2007 R2 Std in my Lab. One server.
2. Updated it with the latest CU. UPDATE DATABASE FIRST! (http://www.microsoft.com/en-us/download/details.aspx?id=19178)
3. Download the latest firmware for LG 8540 for OCS 2007 R2 (3.5.6907.222 (1.23)) (http://www.microsoft.com/en-us/download/details.aspx?id=1777)
4. Install the update and approved it as described here: http://blogs.technet.com/b/ucspotting/archive/2009/03/11/troubleshooting-ocs-2007-r2-device-update-service-for-communicator-phone-edition.aspx
5. Start the device and logged in as “domain.com\username” not just domain\username here is why: http://theucguy.wordpress.com/2009/02/20/tanjay-lg-nortel-cannot-download-certificate-because-domain-is-not-accessible-if-the-problem-persists-contact-your-system-administrator/
7. Nothing happened – no updates! 
8. tried to get update using IE /DeviceUpdateFiles_Int/UCPhone/LG-Nortel/IP8540/A/ENU/3.5.6907.0/CPE/CPE.nbt">http://<OCS FQDN>/DeviceUpdateFiles_Int/UCPhone/LG-Nortel/IP8540/A/ENU/
3.5.6907.0/CPE/CPE.nbt – got a blank page instead of the file.
8.1. Static Content feature was missed from IIS installation – installed it. Still nothing
8.2 Removed <mimeMap fileExtension=".cat" mimeType="binary/octet-stream" /> from c:\windows\system32\inetsrv\configuration\applicationHost.config and rebooted the server (just iisreset did not help)– I can download file successfully now. The solution was found here: http://www.ocspedia.com/Misc/Update_Server_Check_List_R2.aspx
9. So do the device – successfully got the update.
10. I can monitor it in log files (I am using CMTRACE.exe from SCCM to see logs “live”)
:
11.As soon as the device was updated to 3.5.6907.222 I plugged the phone to my production network hoping it will accept 4.0.7555.4066 I have downloaded and approved for Lync as described in a nice Jeff’s article. Unfortunately it did not happened
12. Some research leaded me to that thread and I realized I am not alone. It looks like due to cert issue LG 8540 cannot get the latest and greatest firmware (CU6, June 2012) and need to be upgraded to a previous (CU5, March 2012). The problem is the patch is not available anymore! All links point to CU6 even from CU5 KB. Luckily Lync15 posted a link to his SkyDrive where he uploaded the old CU5. Whole thread is here direct link is here. Problem in details is described by Jeff here. Thank you guys!
13. I removed the latest firmware for LG 8540 from my Lync and published CU5 instead:
14. Restarted the phone and it successfully got 4.0.7577.4066 from Lync.
15. Now we can add CU6 Lync Device Updater and LG 8540 accepts it.
Reference: Jeff on Lync Phone Troubleshooting: http://blog.schertz.name/2012/03/troubleshooting-lync-phone-edition-issues/
IT Consultant Everyday Notes 