Ok number one no you dont need to put a data plan on that phone. I have the Blackjack and I worked at AT&T and its is not required for text messages. Unfortunately you are looking at doing a master reset. It sounds to me that your OS is running into some errors. If that doesnt work you might be needing to reload your OS. Although if you have already done that and it is still giving you the same problem then you might want to call and find out if you can warranty it. If you do a master reset and are familiar with Active Sync I would try to back up your data so you dont lose anything.