Most people spend a reasonable amount of time looking for their next mobile phone, checking prices, comparing specifications, looking at the different offers from competing carriers.
How many of those people give any thought whatsoever to their old phone? Quite a few, but not nearly everyone. A lot of people keep their old phone as a spare, pack it away somewhere and forget about it. Having a spare may seem like a good idea at the time, but often SIM cards from newer phones are not compatible with older phones, so if your new phone breaks down switching back to your “spare” may not be as easy as you thought. Other considerations are that if you have insurance, or your network offers this service free then you may already have 24 hour replacement for lost, stolen or damaged phones, in which case you really don’t need that spare sat around gathering dust.
Also keep in mind that with the rate of development in the phone market your phone is a rapidly depreciating asset, you may put away a phone worth £100, and when you come to dispose of it a year or two later it may not be worth anything at all.
So, what should you do? Don’t store it, Sell It! There are many ways to put that old phone to use, you may have a friend or a relative in the market for a cheap pre-owned phone, ask around and see if anyone wants it. Alternatively put it in the classified ads or on ebay and see what you can get for it that way. Alternatively you could give your old phone to charity. Many charities now run recycling programs as a way to raise money, not just on phone but on other consumer electronics as well as ink / toner cartridges. Examples of charities doing this are The Red Cross, Oxfam, Guide Dogs for the Blind, Refuge, Against Breast Cancer and many more. If you donate your phone to one of these organisations they will resell them (or partner with a recycling company) and receive a share of the resulting profits. Alternatively if you just want to get the most cash possible you can use comparison sites like cash for phones which will list prices for your phone from a range of different sellers. Whichever route you choose to take the key thing is to do it sooner rather than later to get the most value back, whether that be for personal use or a charity.
Another important point to note is that selling your phone on has an environmental benefit. Either the useful life of the phone is extended (where the phone is sold as a working pre-owned item to another customer) or it will be scrapped in a responsible way (re-usable materials extracted and toxins properly disposed of).
The very worst thing you can do is leave your phone sat around doing nothing until it is worthless and then throw it in the bin. Not only do you miss out on the opportunity to get / give something back from it, but you will be contributing to some pretty unpleasant pollution as phones which are burned (incinerated) or buried (landfill) release heavy metals including arsenic into the environment… which I am sure you do not want to do!