Correct, the differences you're seeing are purely because of the way reservations are implemented starting with UCCE 7.5(6). As of that version, we no longer make a physical reservation call to the IP phone but just inside UCCE through CTI. Check the 7.5(6) release notes ( http://www.cisco.com/web/software/280840583/28012/Release_Notes_for_ICM_7.5.6.pdf ) for more details.
This design was changed mainly to support the new RT-Lite (69xx) phones as they don't support call waiting,i.e. their busy trigger is fixed at 1, where the old dialer design needed to send the customer call to the agent's phone will the reservation call was still on the phone (however briefly). The added benefit is that there's a little less CUCM configuration to check. And it's actually a lot cleaner this way, I've personally always considered the physical reservation call a bit of a work-around for something that could be done just as well through CTI (like now).
The potential downside is less 'agent awareness' of their reservation, i.e. they no longer see or hear a call on their IP phone to warn them that they are reserved. But then, the same could be said for inbound calls, agents aren't aware that one of those could come up any second either.
From a CTIOS / CAD desktop perspective, you should see no differences between both versions.
