You may not be so excited about your old phone anymore, but chances are that somebody else will be. Apple has programs to recycle your old electronics, including cell phones. Furthermore, Apple recently launched a buy-back program for your iPhone. Get up to $230 for your iPhone 4.
How this helps the environment
Recycling your old phone keeps it and its (likely toxic) battery out of the landfill. Your phone also contains precious metals including copper and silver. If these are recycled, it lessens the demand for mining new metals. The Environmental Protection Agency says that recycling a million phones will reduce greenhouse gases by the same amount as taking 1,368 cars off the road for a year. Apple's buy-back program reduces waste and conserves resources by elongating the lifespan of the product.