You can take a look at the list of Norstar/BCM features documented by E-MetroTel as supported by UCx:
http://www.emetrotel.com/tsd/content/bcm-feature-c...
I am not aware of any documentation that would describe either cosmetic or minor differences in the implementation of these features.

In general, UCx does not use audible notifications as often as BCM did (you get just visual indication on the display). Some people could see it as a benefit (less annoyance for other people around), some people could feel that a confirmation tone is missing. You should sent feedback to E-MetroTel if something like a missing confirmation tone is a frequent complaint from users.

I am pretty sure I know that tone, it's a one normal, one up Norstar tone that was a confirmation tone for enacting DND. It's the same tone that currently exists on the UCx for Ring Again Notification.

There are still quite a few tones that exist from the Norstar/BCM system.

-The familiar single tone Page beep proceeds a page. (It is allowed to be toggled on or off)
-The Ring Again Confirmation tone mentioned above.
-The key clicks on the digital phones
-The 4 Norstar ring tones one the M and T 7000 sets

The error tone, which consisted of the Norstar tone, one normal and one down tone no longer exists.
The Voice Call F66 tone is replaced with the standard Norstar page tone.

A few new tones that you will probably be happy to have are:
-call buzz can be programmed to ring for a call waiting (similar to CS1000/CS2100/M5000sets/Meridian 1 sets.)
-4 additional CS1000 ring tones are available on the Nortel IP Phones.

Voicemail prompts have the same voice as Joan Kenley, the lady who recorded Call Pilot and Meridian Mail.

Some definite improvements with the UCx when compared to the BCM are:

-Internal CLID names do not have a 7 digit limit
-Internal calls can be placed on hold and hold music is heard. (something never available on the Norstar/BCM)
-Incoming Caller ID information can be manipulated, for example, if you want to show that a call came in from IVR, you can program the incoming call to read out "From IVR 3125551212" etc.
-You can add an MGC card and CS1000 and operate the Meridian M2000 and M3900 sets right next to M and T 7000 sets.
-You can switch the phones from showing a Feature key on the lower left corner of the IP Phone displays or switch the IP phones soft keys to read more like a CS1000 with 4 soft keys reading "MSB Redial CFwd Desk"
-The programming of the system is done via a web browser GUI, you can use a PC or a Mac.
-Third party SIP phones can work right next to Nortel telephones
-There are no complicated key codes from the BCM days. Once one license is bought for an extension, it is fully loaded with all features and interchangeable between Unistim, SIP, Digital and analog phones.
-The majority of the feature codes form the Norstar/BCM days still exist.
-SIP trunking, analog trunking and PRI/BRI trunking is a breeze to set up.
-The phone system is designed by the very same people that designed the Nortel BCM/Norstar/Meridian1/CS1000 at Nortel, so you have the very same people who designed your favorite Nortel systems, still engineering a Nortel product today.
-Their market base is rapidly expanding, for examples some big clients are Toys R Us Canada, Large hospitals in the Toronto area, a large school district in Oklahoma, University of Puerto Rico, and many other smaller to mid size businesses around the world, including Australia.
-The price is considerably less than the others product out there today, I've quoted out a few and I believe how inexpensive the system is when compared to the competition out there today.

Those are some of the reasons, I am all UCx and descriptions of the features vs. the BCM. Hope it helps!

Joseph Sus Jr. Nortel Enthusiast
www.joetheucxguy.com