depends how old!! When get an upgrade normally take old one along to CEX/Cash Converters/Generators and see what they want to give me for it which obv depends on how good a condition Ive managed to keep it in!!
I generally keep it as a back up if my new one fails/breaks so I have a spare when I send the new one back. As it usually takes two weeks or so. It's my curse with new phones.
When I then get the next new one I send the older one off to Mazuma, envirofone etc.
I should just send the newer one away as it's worth more and keep the older one as back up really as they're not worth that much after 4 years anyway.
Set it on vibrate and give it to my son's partner. She loves putting it in her knickers and having my son and other mates call. For some reason she never answers.
Don't new phones still always come with a little pre-paid plastic bag that sends then to a charity that either uses them or dis-assembles them for the precious metals and chips ?