CCM 4.1 is built on a Windows Server 2000 platform and has been announced as End of Life. The feature set is getting a little old now and there have been many improvements in the more recent CCM Trains.
CCM 6.x is based on CCM 4.2(3) and incorporates that excellent feature set (on a Linux platform).Most people seem to find the Linux Appliance version of CCM much easier to work with. Upgrades can be done on "split partitions" so rolling back to the previous version is much quicker. The feature set in CCM 6.x is pretty vast and the 6.1(2) version seems to have most of the Bugs worked out (most ;-)
I think most people here would advocate going straight to CCM 6.1(2)
End-of-Sale and End-of-Life Announcement for the Cisco Unified CallManager 4.1
To add to the excellent list, you also have built in Mobility Manager, called Mobility Connect (single reach number), Precense Support, True SIP trunks, SIP stations (SIP Phones). The big one in my opinion is Database Resiliance which means that Subsriber Database is no longer read only and some features previously not available in cases of publisher failure are still present, i.e. Call Forward All, MWI, etc.
I'm not able to access my old voice mail messages all of a sudden. The recording says something like 'the message is currently not available'. This has never happened before in all the years I have been using this system. I have t...