MSISDN of subscriber can be added/set, but never removed
There's a VTY command to add/update the MSISDN of a subscriber, but currently no way to remove the MSISDN of a subscriber once it has been set.
Something like "subscriber (imsi|msisdn|id) IDENT update msisdn none" would be logical compared to the aud2g/aud3g syntax. However, I don't think the VTY parser can deal with choosing between "none" and the free-form string MSSIDN :(
More general VTY logic would be "no subscriber (imsi|msisdn|id) IDENT msisdn", even though the VTY doesn't seem to implement any "no ..." commands at this point.