Here at work, I keep a recycling box under my desk. All of our rechargeable batteries and old cell phones get deposited in to it. Every so often I'll dump it out in the recycling bins at Office Depot.
We have several charities in the area that will take old still usable phones. Most notably one that helps female victims of domestic violence that need to get out of that situation. They can get some basic service and use the old phones to give them a new start.
I donated mine to a woman's shelter. They charge them and give them to women so they have a way to dial 911.
My wife and I donate our phones every two years to Woman's Shelters. Then we take a write off. Greg W.