You can take a screen shot by pressing the home button and your power button at the same time. It will save the screen shot as a picture in your camera roll. From there you can email it to yourself and print it out.
This is what we do.
BFP #1 11/07/2012 EDD 07/09/2013 M/C 11/22/2012
BFP #2 02/05/2013 EDD 09/19/2013
Arrived via c-section 09/27/2013
Put the text where it shows the date, the time, and the actual phone number (not the name stored in your phone), then take a picture of it with a camera (either film or digital). That's what my lawyer has me doing, anyway.
Re: documentation:
Can you take screen shots? I dont know how, but there is a way to do that I thought.
If not, I would take the current newspaper, lay the phone down next to the date and take pictures of the text messages with a camera.
This is what we do.
BFP #1 11/07/2012 EDD 07/09/2013 M/C 11/22/2012
BFP #2 02/05/2013 EDD 09/19/2013 Arrived via c-section 09/27/2013