AT&T is nearly ready to launch a feature that will allow a customer’s smartphone, tablet and other devices to share a single phone number. The feature, now called NumberSync, is a key to making it more attractive for customers to own multiple devices with built-in wireless connections, just as it was important to offer shared data plans. As previously reported by Re/code, AT&T has been testing the underlying technology, code-named Cascade, since at least last year. It was developed in part at the company’s Foundry incubator in Palo Alto, Calif.