At work probably 1 in 20 calls on my phone is actually for me.
I'm in a call group called Support and I only answer those if they ring for 1 minute or more.
As the majority of calls that ring on my phone are for support, when I'm engrossed in work and the phone rings, I don't even look at the screen and so I miss the few internal or DDI calls.
It would make things much better if direct calls to my phone (internal or external) had one ringtone and any calls to my phone from being in a group could have a different ringtone.
It seems this isn't possible at the moment, but I hoe it could be added, as I reckon a lot of people could benefit from it.