As I understand it, since App Store purchases are tied to an Apple ID and cannot be transferred, your apps will definitely be lost. If you are storing your pictures with iCloud Photo Library, they may be lost as well. If they are only on your iPhone they may be OK. In any case, I would archive them to a computer:
Import photos and videos from your iPhone, iPad, or iPod touch - Apple Support
I believe SMS/MMS messages are tied to your phone number only, so they should be OK as well. I'm not sure about iMessages.
About iMessage and SMS/MMS - Apple Support