When you plug your iPhone/iTouch/iPad into your computer and run iTunes, there are three forms of communication that you can request happen between your computer and the device: syncing, backing up, and transferring purchases.
Syncing happens much more frequently; when your device is syncing, iTunes is making sure that the data on your computer and your phone are up-to-date with each other. Typically, this involves copying music or apps you have purchased on your computer to your device, making sure your calendars and address books match, and stuff like that. When iTunes syncs your device, it does not make a backup -- this is the surprise that bites most of us later.
In the syncing description, I said that syncing copies music and apps that you've purchased on your computer to your device -- note that I didn't say a word about the other direction! If you purchase music and/or apps on your device, occasionally you'll want to make sure these purchases are copied to iTunes on your computer in case something happens to your device. To copy your purchases, right-click on the device under "Devices" in the main iTunes window and click "Transfer Purchases". I just did this myself and had five songs and twelve apps that I needed to copy to iTunes.
Backing-Up Your Texts/VoicemailsDecipher TextMessage and Decipher VoiceMail come in -- our software reads the iTunes backup files and makes its own history of your messages, including images, videos, and other files sent via MMS, so that you can view, save, copy, and print messages as you need them. I enjoy keeping my messages (especially my SMS messages) backed-up this way, because I can actually browse through the history -- read old messages between my husband and I when were dating, look at photos my friends sent me, and copy-out information that I realized I never did put to use :)
I hope this little post on data protection has been helpful to you. If you have questions, we encourage you to post them here or email us.