I'm not so sure of that. A quick search put the figure at just 3.4% of GDP [1].
Even if a lot of sales do happen online, many of them could shift back to phone calls relatively easily.
Obviously there would be a significant impact, but I think the Internet is still a long way away from being something that simply can't be turned off.
I was more referring to credit card transactions at just about any store. Even if the store's processing machine uses dial-up, there's a good chance that the vendor's backend is dependent on an Internet connection.
I admit that this is biased towards the West, and it's possible that in places Egypt cash might be more popular than it is in the West.
That's just one small piece of the puzzle though. You also have to think about sales that take place through email communication. You have to think about stocks being bought/sold online. Not that some of these things can't be replaced by more primitive means, but that is an undeniable huge hit to an economy that has to suddenly adjust to do things by analog means.
