For the UK there's http://www.envirofone.com/ http://www.envirofone.com/ or http://www.mazumamobile.com/ http://www.mazumamobile.com/ or http://www.fonebank.com

For the UK there's http://www.envirofone.com/ http://www.envirofone.com/ or http://www.mazumamobile.com/ http://www.mazumamobile.com/ or http://www.fonebank.com/ http://www.fonebank.com/ amongst others. I've used the first 2 with excellent results. Obviously you get slightly less than selling on the open market, but you don't have to deal with scammers, and get the cash quickly and without issues.