UK households are failing to cash in on around £3.4 billion worth of old mobile phones, according to research.
Virtual operator Giffgaff, which published the study, said trading in a recyclable used handset makes £111 on average.
Exact prices vary between models and can fall quickly with age but even a small amount could help amid the cost of living crisis, it added.
Research suggests 45 per cent of people have a "backup" mobile phone they rarely use in addition to their day-to-day device.
Around two in three (67 per cent) of those with spare handsets say they have not used them in the past year and nearly a fifth (19 per cent) have used their previous device just once in that time.
Some people also have feelings of fondness for their old mobiles that are stopping them from letting go, with 12 per cent saying they feel emotionally attached to their previous phone.
Alongside the financial hit, not recycling an old mobile phone could contribute to the problem of electronic waste from old, unused tech, Giffgaff said.
A report published by the UN in 2020 found the UK generated the second-highest amount of e-waste per person in the world, after Norway, at 23.9kg. This far exceeded the world average of 7.3 kg per capita and the European average of 16.2kg.
MoneySavingExpert advises people to shop around and use an online comparison tool before deciding where to trade in their devices.
Giffgaff chief executive Ash Schofield said: “Our latest research highlights that there’s a significant opportunity for people with an old mobile phone to make a tangible, sustainable impact, and gain some extra cash.
“And with the cost of living rising across the board, now is a great time to get something back by trading in your old phone.”
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