I recently upgraded from 3.3(4)sr2 to 4.x with unity on a separate server. Are you running CM and Unity on different servers? I made sure of the following before upgrading:
- Latest SR and OS kits
- Latest version of BARS installed with backups performed and kept a couple backups of previous version
- If you have the hardware create a test lab and restore your backups just to test and also test the upgrade.
- If possible create a disk image using something like ghost etc.
Create check list of items to test such as:
- Phone registrations
- Indial / out dial
- Voice mail functionality, forwarding, and accessibility
- Attendant console
etc etc..
- Upgrade the TSP for Unity on the unity server
I also found that there were little differences with route lists/ groups the upgrade created additional call manager groups with them, double check that.
As for the Ericsson try the interoperability portal
http://www.cisco.com/warp/public/779/largeent/avvid/inter_operability/
Hope this is of some help, good luck.