Deleted text messages; how to recover.

I am wondering if its possible to recover deleted text msgs from my iphone. I don't back up my phone often so my last backup was about 3 weeks ago so does that mean if I restore to that back up, I can only get msgs that was in that backup? If so, does that mean if I restore to that backup, all those msgs will be blended with the ones in my phone currently?

Another question: If I backup my phone right now, does that mean the deleted msgs are also backup? Which then I can restore to the backup with all msgs included.