Question: Which entity can initiate an in-call modification procedure to change the call mode?
Option 1: Either side of the radio interface
Option 2: Only the User Equipment (UE)
Option 3: Only the Network
Option 4: The Serving and System Architecture Evolution (SAE) Gateway
Explanation: According to the in-call modification procedures, either side of the radio interface can act as the requesting user to invoke the in-call modification. This means that both the User Equipment (UE) and the Network have the capability to initiate a change in call mode.