Sustainable designers look for ways to design appropriate components that can be exchanged so that the product as a whole can endure longer. Perhaps a mobile phone’s case gets marred over time, having been dropped too many times or from swimming in a purse or pocket with keys, coins, and other hard-edged objects. There are several potential solutions here that could increase the life of the phone:
• Make the case out of more durable, scratch – resistant, or colorfast materials.
• Make the case out of materials that age gracefully or create a desired patina (like wood or denim). 
added benefit of enabling customization and protects the components from the whims of trends.
• Standardize components so they can be used in many different models, increasing the lifespan of the subsystem even when the software, casing, or other components change over time.
• Design devices to be expandable, even just a bit, allowing other devices to be added or attached as they become available or change.
• Transmaterialize the functions, where possible, so that the physical device can outlast changes in features and interface without requiring a redesign.
Strangely, solutions like snap-on cases of different colors and patterns have been around for years now, but still many phone models are designed without them. This is a shame.