Question: What is the default Number Plan Identification (NPI) for Called Number Fields if all digits are in the range 0-9, according to 3GPP specifications?
Option 1: ITU-T E.164
Option 2: National Numbering Plan
Option 3: Unknown NPI
Option 4: Manufacturer Defined NPI
Explanation: The default NPI is set to ITU-T E.164 when all digits of the called number are within the range 0-9, ensuring compatibility with international numbering standards for voice and data services. This setting facilitates seamless communication across different networks, especially during roaming scenarios, by adhering to a universally recognized numbering plan.