Not seven, not eight, but nine digits after the area code. That’s what dialing a cellphone number will look like for the 22 million people who share the same area code in the giant metropolitan area of São Paulo, Brazil. And that’s because they simply ran out of combinations for the existing eight-digit format there. Being the economic engine of a booming Brazilian economy, São Paulo already has more than 40 million mobile numbers. All of Canada, by comparison, has about 25 million; adding the extra digit instead of creating more area codes was the way Brazilian authorities decided to avoid confusion between local and long-distance calls for the people of the 64 municipalities that make up greater São Paulo and its surroundings. While users will have their calls rerouted automatically for six months as they get used to the changes, mobile phone companies will pick up the $180-million tab to implement the new numbering system. It may seem expensive, but in fact it’s a sound investment for these companies that have to keep up with São Paulo’s current appetite for phones, tablets and other mobile gadgets: 340,000 new numbers every month.