Smartphone turnover can be rapid. Most of us have upgraded at least once and have an old device or two lying around. If you need a project this weekend, make yours useful again.
For Your Home
One of the most obvious uses for an old smartphone is, well, to use it as a phone. You can download a VOIP app suchh Skype and use it as a home-based handset. You could even use it as a webcam if you'd prefer.
A less-exciting but valid option is to turn your smartphone into a remote. Just about every set top box with a network connection offers a smartphone app to control it. If your old smartphone has an infrared transmitter, you can search its app store for a universal remote app and control just about anything. Your old smartphone also makes for a great backup alarm clock (here are our app suggestions for Android and iOS). Because there are so many alarm apps to choose from, you can easily pick one that suits your needs and tastes.
For Your Car
Any phone can call emergency numbers even without a SIM, so carrying a spare in your car can make for a useful emergency phone. If your car parks in range of your home's Wi-Fi, you can sync music to your phone automatically. Use iTunes Wi-Fi sync for iPhones and Doubletwist for Android.
On The Go
My favourite use of an old smartphone (or tablet, for that matter) is to create a portable gaming device. A jailbroken iDevice works OK, but Android offers so many fantastic options in the retro gaming department. While there may be more practical solutions, a retro gaming device is probably the most fun.
If you're a photographer (professional or otherwise), you can turn your old smartphone into a powerful camera remote. If your camera has a Live View mode, you might even be able to see what your camera sees directly from your app of choice (there are a few to pick). Even if photography is just a hobby, this can be a lot of fun and you can take some interesting pictures you'd might otherwise be unable to get.
Need some suggestions for tablets instead of smartphones? Read this, and have a great weekend!