How to recover my iphone text conversations?

Today I went to send a text message and when I opened my messaging app, all of my texts conversations were gone! I never delete my messages so this was quite a shock. Is there any way for me to get them all back? I've had a software update waiting for me for a couple of days, but it says it was to fix email bugs so I don't know if this has anything to do with it or not. Any help would be appreciated!

Reset your phone to a previous day or shut your phone off & turn it on again.