Question: What action may the network take upon receiving a START DTMF message from the mobile station?
Option 1: The network will always convert the received digit into a DTMF tone and apply it toward the remote user.
Option 2: The network may either convert the received digit into a DTMF tone or send the DTMF digit as an out-of-band message and return a START DTMF ACKNOWLEDGE message to the mobile station.
Option 3: The network will always reject the START DTMF message and send a START DTMF REJECT message to the mobile station.
Option 4: The network will ignore the START DTMF message and not take any action.
Explanation: According to the specification, upon receiving a START DTMF message, the network has two possible actions: converting the received digit into a DTMF tone or sending the DTMF digit as an out-of-band message and returning a START DTMF ACKNOWLEDGE message. This allows for flexibility in handling DTMF messages and provides feedback to the mobile station.