As I recall, NAI in SS7 set as TON (Type of Number) in VoIP environments. This field is called "Callled Party Numbering Type" (or Calling Party) in CUCM. Is this what you are looking for?
There are a number of places this field can be set in CUCM, and can also be set on a router using voice translation profiles. What object are you configuring in CUCM? An MGCP gateway? H323 gateway? Transformation pattern? Translation pattern? Route Pattern?
