The Micromax X259 Solar Phone has a large solar panel on the back which is used to recharge the batteries. The bummer is that it is currently only in India.
The Micromax X259 has a 2.4-inch QVGA screen (240 x 320p), a VGA camera, and a 4.5 hour talk time per charge. The solar panel will give you about 1.5 hours of talk time per 3 hours of sun charging.