I am afraid I do not know what use they are BUT I was also happy to donate and took along 20 empty cartridges only to find that they do not take Epson !
Many of the 'compatible' cartridges you can buy for inkjet printers are manufactured using recycled cartridges. Charities sell your donated cartridges to these manufacturers.
Mobile phones are sold to recyclers, who recover the valuable copper, gold, palladium and platinum (as well as less valuable metals, such as iron and aluminium) from the phones: http://www.nokia.com/A4211216