Question: In an SMS using basic text formatting as per 3GPP specifications, what is the primary purpose of setting `TP-UDHI=1` in the message header?
Option 1: To indicate the use of a predefined sound within the message.
Option 2: To signal the presence of a User Data Header (UDH) for formatting options.
Option 3: To specify the character encoding scheme for the SMS User Data.
Option 4: To enable bold text formatting for a portion of the message.
Explanation: Setting `TP-UDHI=1` (TP-UDHI: TP-User Data Header Indicator) signals to the receiving device that the SMS contains a User Data Header (UDH), which in turn, may include various formatting instructions such as bold text, predefined sounds, or other enhancements. This indicator is crucial for the proper interpretation and display of formatted messages.