My Mama bought a K500i. Nice thingy. A gazillion more features than shell ever use but thats modern technique and not-so-modern elderly for you...
Im personally very partial to the Sony Ericssons, having a K300i myself. Of course, the fact that the K500i is not that much different from mine did not at all influence my advice when Mama bought hers. Since I knew beforehand that I was the one who had to program the thingy...

But the S-series ? Dont like them. Not enough buttons.