Just upgrade my lab UCM to 220.127.116.1100-6 and trying out some new features. One of them is the new Enhanced Line Mode on the 8800 series phone. Previously you can only use the 5 keys on the left as programmable line keys, and the 5 keys on the right are session keys and not programmable. With Enhanced Line mode, you can convert the 5 session keys into programmable line keys as well.
Firmware version in my lab:
This is the device specific configuration under my 8861 phone. The list configuration item is the new Line Mode feature.
There is a warning for you that certain features will be missing if you configured your phones in ELM.
After that you will see all 10 keys are now programmable!
Just to randomly configure some features there...
And this is how the phone looks like: