The latching/locking mechanism is a bunch of steel rods inside the door that couple all the bits together. At a few points they're "hinged" by plastic bits. One of the plastic bits has broken.
When it happened to me, I was lucky that I could open it from the outside. You need to get the door open in order to be able to remove the inside side panel in order to find & replace the broken bit. Most likely what's happened is the lock itself is stuck. Your best bet is to take it to a dealer and have them try to open it, perhaps using a slimjim or something.
Currently: '05 Camry XLE (wrapped the '98 around a deer); '00 Sienna LE; Toyota owner (just about every model) since youth.