HTC One User Manual page 165

Protecting a message from being deleted
You can lock a message so that it will not be deleted even if you delete the
other messages in the conversation.
1. On the All messages screen, tap a contact (or phone number) to
display the exchange of messages with that contact.
2. Tap the message that you want to lock.
3. Tap Lock message on the options menu. A lock icon
displayed.
Messages 165
is