Thanks Merlin!
We changed only the NBX (from 3000 analog to 3001R), telephones remain the same.
We used the same database backup from 3000 Analog and we restored it on the 3001R!
The missed calls appear in the call log, but the issue is that when the phone has new missed calls (for example one missed call or two missed calls)the LCD does not alert the user "You have 2 Missed Calls"! The user has to regularly check for missed calls in the Call Log!
Besides this issue, everything looks fine and working!
In case I suspect the software of the phone, How can I force the phone to download the latest software from the NBX!