The choice of servers for IPCC express is completely independent from Callmanager hardware. Regarding the servers in the CCM cluster being the same, its generally a good practice to keep them all the same. (Though, you definitely can have a 7835 for your Subscriber and 7845 for Publisher, no big deal).
Now for IPCC Express, the choice of server requirement is based on, many factors.
a. Just like Callmanager assigns weights to devices, IPCC Express assigns weights or points to various features such as (number of Recording sessions, number of Historical reporting sessions, ASR/TTS, total number of agents, supervisors, IVR ports etc. If your server doesnt meet the total number of points required for all the features you need, then you need to use the next higher model. So a 7825 has 900 points, 7835 has 1266 points, 7845 has i think about 3400 points. You have to use a spreadsheet available for download (called CRS configuration tool) which tells you the right hardware you need for the IPCC features that is required for your call center.
7845s are same as 7835s except that 7845s have dual processors, 2 extra hard disks, RAID 5 etc. You may need a 7845 if you need upto two HR sessions during business hours.
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...