After some time, changing your smartphone or PC, shouldn't be considered as a want, but more like a need. After 4 or 5 years, the device that you bought should be already way behind technologically, compared to other devices on the market. So, the question is, how often should you change it? If we take as an example an Iphone, the right time to change it would be around 3 years, because that is the moment where the phone starts to lose quite a bit in value, performance and battery life. Of course, it will value more if kept in good shape throughout those years and will bring you some bucks for a new purchase, but if you change it after 3 years, for 6 years, it will make you an extra of around $100-$200, which is worth it. Also, for PC's keep in mind that older technologies are less power efficient after a while, so replacing them will also result in less electricity consumed overall, which I think it is worth the investment in order to reduce your carbon footprint.

I agree with this completely. The unfortunate thing is that companies such as Apple are releasing multiple phones within only a few years, occasionally changing the cables so that you cannot charge older phones with newer cables if you break your old one, consequently requiring us to purchase a newer phone. Even if it isn't necessarily a need at the time to buy a new phone, it becomes one once you can no longer use it to an extent, increasing our carbon footprint in a situation where it could be reduced by not making the purchase.