The LG phones seems to have a problem. You can forward the text message to an email system by simply using the forward option once the txt msg is open however it doesn't contain the sender's information. (i.e. commonly referred to as a header).
Some messages that may have been forwarded to you for example that contain other information from a series of senders is also problematic as you have only 160 characters and it typically requires mutliple forwards.
Again, it doesn't contain "header" information... just the text message.
If someone finds a solution, do post. In case of subpoenas, I'm informed by Verizon support the only information (using phone txting) that is kept is at the "header" level (and their are timeframes in play) but the details of the msg is not kept.
Just screenshot them with time stamps/ mdated showing. To go a step further, if they are saved in your contacts-remove them that way their cell number shows instead of their name. That way it cannot be disputed or misconstrued, at all!