If your old cellphone are running and in good condition you can use it as a back up. Don't throw it, maybe you can use it some other time. If you can't do that, maybe you can donate it to the one who need a cellphone badly.
If they're still working you should sell them online or if you want look for stores in your area that buys second-hand phones because we do have lots of those in my place. If you want, giv them to your kids or some close that wants to have one.