http://www.usedcellphones.com/storefront/index.cfm
http://ask.metafilter.com/16276/Can-I-purchase-a-used-cell-phone
yard sales, flea markets
If you are looking for an internet source, you can try http://www.sell.com
u can try amazon.com u can also try ubid.com (which is like ebay just not as well known).
http://www.usedcellphones.com/storefront/index.cfm
http://ask.metafilter.com/16276/Can-I-purchase-a-used-cell-phone
yard sales, flea markets
If you are looking for an internet source, you can try http://www.sell.com
u can try amazon.com u can also try ubid.com (which is like ebay just not as well known).