I think it would be a nice feature, to have a phone directory in the pbx. Maybe we could also transfer these entries to the IP phones, to have an all phonesthe same phone directory.
In case of an incoming call, the caller's name could be added and presented to the phone (either by the pbx or the ringing phone itself could show the name from the local downloaded directory).
I have worked with a software based ip pbx with lookups also to external sql databases and it was very helpful, especially for customers with sales or support departments.