I've read that the solar chargers do not kick out enough power to fully charge cell phones, it might get it to about 80% of the cell phone's battery supply but can't recharge the battery past that. The problem is these rechargeable batteries build a "memory" of how it recharges and you'll start damaging your cell phones charge longevity - which might matter to you on normal days of normal usage -
Portable Solar Battery Charger | Portable Solar Panels | Off-Grid Solar Generators | Goal Zero - Extreme Portable Power
--- I've seen surfers use these on crazy long backpacking trips to keep phones and cameras charged. --- They rave about how great it works, however I'm not sure if they're endorsed by the company for the trip or being totally honest.
However, they seem to have a pretty high capacity