As we approach the phone event horizon...
As a society sinks into depression, the people of the society need to cheer themselves up by buying themselves gifts. This is usually done through the purchase of mobile telephones. As more money is spent on mobile telephones, more phone shops are built, and the quality of the phones begins to diminish as the demand for different types of phone increases. This makes people buy more phones.
The above turns into a vicious cycle, the end result being that other industries begin to falter.
Eventually the titular Mobile Telephone Event Horizon is reached, where the only type of store economically viable to build is a phone shop. At this point, society ceases to function, and the economy collapses, sending a world into ruin. In the case of Britain, the population forsook mobile telephones and evolved into ham radio operators.
Or something like that. Mine's the one with the starship Heart of Gold in the pocket...