Your old cell phone is more precious than you think: it contains gold, used in contacts and microcircuits.
Electronic devices such as mobile phones use extremely low voltages and currents, easily disturbed by corrosion of conductive materials.
Gold solves this problem: it conducts electricity efficiently and is immune to corrosion. That's why it is present in virtually any electronic device that you can think of.
It is necessary about 1 ton of gold rich ore of a mine to get 1 g pure of this metal. Instead, it's enough to use 40 cell phones to get the same amount.