When iOS 9 is released this fall you'll be able to answer phone calls on your iPad or Mac even if you left your iPhone at home. Continuity, the feature that currently lets you make and answer calls from most of your Apple devices on the same network, will add the ability to do the same over a cellular connection, and that means forgetting your iPhone when you go to the coffee shop won't lead to missed calls.
iOS lets you answer calls from your iPad or Mac when you forget your iPhone at home
Freeing devices from being on the same WiFi network adds a new flexibility to the devices we take out of the office or our homes. Currently, our iPhones are a sort of communication nexus or hub, but only when the iPads and Macs they link to are on the same network. Once that connection is gone, our devices are essentially isolated from each other.
Continuity's new cellular support is already working in the beta version of iOS 9 available to developers, and presumably will still be working when the public beta rolls out in July.
The catch is that cell service providers have to support the feature, and so far only T-Mobile has said it will. AT&T, Verizon, and Sprint will likely follow suit although they may very well drag their feet, just as they have done with supporting cellular calls over WiFi.
iOS 9 was unveiled on Monday during Apple's Worldwide Developer Conference keynote event. The update will be free and available this fall with support every device capable of running iOS 8.
[Thanks to The Verge for the heads up]