I've bought such a wind up torch for about 6 quid. At start it was ok but the battery inside doesn't work so good anymore so I need to wind up a lot to get not very much light. Also I have to wind up a lot just to be able to call 30 secs with a nokia 3330 phone.
I think it's not worth it. Neither is it more environmentally friendly then just using rechargeable batteries in your flashlight. Because it's made of plastic, it's quite big, it got a battery inside (not replacable, so of it dies you throw it all away), ... Just carrying a small flashlight with extra batteries takes up less space and weight - and gives more light. Or just using a candle lantern, oil lantern...
You can get solar rechargers or something to put AA batteries in to charge up the mobile phone. But what I just do is turning off the mobile and only now and then turning it on to check for messages. That's smarter I think.
Just my idea..