> A computer is now an essential way to get things done in the modern world and to participate in the market economy.
I would say Internet is the essential way, not computers. Take the Internet out and the equation changes completely and you can't do much without it. Take the computers out, it still remains a valid statement.
You can use any devices you want to get on the Internet; computers, smartphones, tablets, and so on. It is up to you and you do not "need" any specific device, you "want" the smartphone because it is the most convenient portable device you can use.
Do everyone need computers? No, do everyone need Internet? Most yes, it may be the only way to pay bills for some, it may be the only way to securely communicate in an oppressive country, and so on.
You can use libraries to get access to the Internet without owning any of the electronics. So, no, people don't need these devices but they may need the Internet and they want the devices to make their life easier.