Default How to turn off auto delete of txt message.

As I was going through the setting, I can't seem to find the option to keep all of my txt msg. The phone limit my txt to 999 messages per thread. I usally archive all of my txt msg on the captivate. There is an option in the messages setting to turn off the auto delete but I can't seem to find it on the atrix. Is there a hack or app that allow me to have all my txt stay on the phone?

Sent from my MB860