How about a Firefly? See link: [broken link removed]
I know they're designed with children in mind, but this seems to fit most of your criteria. It's uncomplicated by music players, cameras, and all the other stuff that comes with mobiles these days. There are 2 big speed-dial buttons on the front that can be assigned to specific numbers, and it's sim-free, meaning you can shop around for the best deal on any of the networks. The only downside that I can see is the initial cost: €99.