How can I prevent my device from automatically converting SMS to MMS? The Galaxy S I9000 messaging app automatically converts long SMS messages to MMS. How can I disable this?
You can't do so with your samsung official messaging application, all of what you can get is a pop notification that you are now in the MMS zone (Converting to multimedia message...).

I would recommend Handcent SMS application, available at the market, and has an option for not converting texts (SMS) into MMS