Question: What is implied by the provision of telecommunication services in a 3GPP system, aside from subscription to basic and possibly supplementary services?
Option 1: Compatibility between User Equipment (UE) and successful call establishment without network verification.
Option 2: Registration into a service directory and compatibility between terminals.
Option 3: Interworking capabilities with non-3GPP networks only, without any terminal compatibility checks.
Option 4: Mandatory subscription to supplementary services for all users.
Explanation: The provision of telecommunication services in a 3GPP system involves more than just service subscriptions. Two key aspects implied are the need for registration into a service directory (ensuring users can be identified and reached within the network) and compatibility between terminals (guaranteeing that different devices can effectively communicate with each other).