You may not give WhatsApp a second glance in the App Store, but in other countries, it's the messaging app of choice. It's so big in Mexico, for instance, that Walmart Mexico is now accepting grocery delivery orders for its Superama supermarkets sent via the messaging service. According to Reuters, customers can send their orders through WhatsApp to a number owned by Walmart -- they don't even have to type their list out. The publication tested it by sending the number a photo of a handwritten list and got a response from a representative immediately.