I've seen a post or two talking about these, and it was my same intentions to back them up to my computer. There is no normal way to do it, increase memory for them etc. Emailing them is very time consuming, and I am only lucky to have unlimited texts to consider that an option. I wanted to find a solution by dealing directly with the files, which might be difficult but would solve this problem.
As it starts, I've had trouble using Bitpim on this phone, have of its features worked on my old one, not including SMS, but I can't even get filesystem access to it like some of you had. Well luckily I got the appropriate programs a drivers, through a lot of searching, which may still be incomplete. I have QPST, QXDM, Samsung PST, and a BREW SDK Tools.
Mostly through the use of the EFS Explorer I found some relevant paths: "/msgs/mms/" and "/nvm/sms_wp_os/".
The second holds a file for about every text message I ave stored, and possibly a few extra. The weird thing about this is it may not hold all the information in each file. The first may have that information, but the messages it stores are lumped together in only a handful of files, and the ordering maybe be a bit erratic.
So I was looking to parse these files so I would have to read it from the screen or take a picture of such for every message, every time. I was wondering of any luck other people have had backing up text messages.