When looking at the text the tim is listed to the upper right hand corner of each text. If you turn the phone off all that will be listed is the date the message was received. Hope this helps.
There is a patch for this at precentral.net. It is called "Timestamps - Clean". If you have not discovered the wonderful world of homebrew apps and patches available at precentral you owe it to yourself and your phone to check it out. I was unsure about doing it at first but Palm has encouraged homebrew for the phone and one of their techs assured me that I would not void my warranty by installing them (although Palm has indicated they might not be so forgiving with the overclock patches). I highly recommend that you look into the many things you can do for your phone that will make it even better!