[cisco-voip] Upgrading CM 3.3(5) to 4.1(3) ?

[TechGuy]

I will be performing an upgrade on CM in a couple of weeks.  Going to
go from 3.3(5) to 4.1(3).  I have done this upgrade before at a
previous employer but much more nervous about this one due to the
shear size of the deployment.  I am nervous about the end user affect
/ fallout to be honest.

Here they are setup with each line in a partition, such as Line 1 in
"PAR_Line_1" and Line 2 "PAR_Line_2" they do this to forward line 1 to
line 2 if line 1 is busy or something.  Now in 4.1(3) each line can
support multiple calls so it changes things a bit.

Anyone have any docs on what is changed and how it affects the end
users?  How did you manage alot of this?  Just curious.

Thanks!