I have done the iOS 7.1.2 upgrade in my iPhone 4 recently. My iPhone was pretty stable with the iOS 6.0.1. Due to some mandatory requirement for the OS upgrade I have performed the iOS 7 upgrade. After upgrading my iPhone 4 to iOS 7, I feel there are lot of positives and negatives. The iOS 7 gives new look and feel to the phone but I lost my stability with the phone. Lot of performance issues started with the phone like it won’t respond to our touches as looks like the phone is quite busy. Sometimes the apps are getting crashes.The other issue I faced is that I had lot of old messages (SMS) in my phone and none of them are getting indexed after the iOS 7 upgrade. The old messages are not showing the Spotlight search results. But this I fixed by resetting the phone and restore.
Step 1: Take a backup with iTunes. Check the last backup status in preference menu -> devices tab
Step 2: Remove the phone from system and Go to iPhone -> settings ->General -> Reset -> Erase All Content and Settings. It will ask for phone password and confirmation. This process will take some time to complete (around 5 mins)
Step 3: After that Connect to the iPhone to iTunes and restore from the iTunes backup.
After this restore you will have all the messages (including old) in your phone and it will be automatically indexed by the spotlight search.