If the other line is using Verizon Message+ and Integrated Messaging is activated, then you can log in to MyVerizon using the other lines' profile login using a browser and access the Message+ desktop app or webapp to see the messages. You won't see iMessages this way though.
Kayla,414T, that is a great question! To see the contents of the text message, you would need to contact a lawyer to receive a subpoena. Then, they would receive text message details. With our Smart Family feature, you can see who is texting who, at what times, and more. Does this information help? MichelleH_VZW