It is easy. It really is.
If you are experiencing weird issues with SMS and/or email sorting after upgrading to 1.1.3, this is for you. I've seen many complaints around the net on this issue and even Apple seem to struggle on it.
My guess: this is a *real* bug Apple left out when released the update.
SYMPTOMS: after upgrading to 1.1.3, when you receive a SMS the timestamp is wrong and therefore it's placed out of order in conversation.
DETAIL: you don't live on the West Coast and all received SMSs have a fixed time offset. Guess what? It's what's between you and Cupertino.
CAUSE: the timezone database in firmware 1.1.3 has wrong default permissions for user "mobile". After upgrading to 1.1.3 your timezone may default to Cupertino, especially if you had to rollback from Nate True's and downgrade to 1.1.1. You try and set it back to the right zone but system time doesn't change. Then you tune system time to your own and voilą, you created an offset between you and the system (which still believes it's Cupertino time) fooling the phone and yourself.
SOLUTION: turn on WiFi on the iPhone, ssh yourself into the system and fix timezone database permission:
chmod 777 /var/db/timezone
Then enter Settings / Date&Time and change your timezone back and forth, you'll notice system time will immediately follow accordingly (that was NOT true before the fix). Set timezone to your own, correct system time to reflect your time and you're done.
Kudos to kopernicus and Hawkman of hackint0sh forum who suggested this
