I'm afraid this feature does currently not exist within the Convergence product. There is however an RFE/ER open on this :
12235033 : Enable advanced personal address book functionality (creation/deletion/sharing)
The request is however not public available in MOS to be tracked.
If you want to be added to this RFE as an interested party , then you will have to open a Service Request so we can link you to it.
Currently, when exactly this feature is going to be implemented is unknown.
The above can also be found in the KM doc :
Can Personal Address Books Be Shared Between Users In Convergence ? (Doc ID 1320023.1)