Locking text messages

The lock option is available for content on this phone such as pictures, videos, text messages, and contacts. As best as I can tell, locking any of those just prevents you from erasing that content when you select the Erase option on the phone.

However, I don't think the lock option would prevent content from being erased if you chose 'Settings & Tools' -> 'Phone Settings' -> 'Security' -> 'Restore Phone'

I need to digress for just a moment. For Messages, you have two ways of organizing your messages. Under messages, select "9. Settings". Under 'Inbox View', you can organize the messages according to 'Time' or 'Contact'.

If the messages are organized according to 'Time', then while you are reading the content of one of your messages select 'Options' in the lower right corner and then select 'Lock'

If the messages are organized according to 'Contact', the steps are slightly different to lock the messages. I have two messages saved from Google's 411 service. When I tap on the name of the 411Google message Contact, I see a partial view of the contents of both text messages which are divided by a thin horizontal bar. Tapping the area above or below that horizontal bar causes the phone not only to reveal the entire content of that message, but it also now makes available the option in the lower right corner called "Options" so that I can lock the message.