Apple released a new beta version of its iOS 9 mobile operating system to developers today, and, among other things, it includes support for Wi-Fi calling from AT&T and Sprint.

Cellular carriers are interested in allowing subscribers to make calls via Wi-Fi because it takes some pressure off already-overworked data networks. Subscribers like it because it costs less and increases call reliability.

So Apple has built this option into its mobile OS (release notes). Sprint and AT&T have made no official announcements about offering Wi-Fi calling, but they likely will soon. T-Mobile customers have been using Wi-Fi calling for some time now.

Apple has also added a cool little feature called “Wi-Fi Assist” that prevents iPhones from connecting to poor-performing Wi-Fi networks. The feature might prevent a phone from switching a call from cellular to Wi-fi if the Wi-Fi signal does not exceed a certain strength threshold.

The new beta release — the fifth — adds 15 new wallpapers that show off the iPhone’s display. It also phases out some of the older, less graphically robust, wallpapers.

The new beta also includes a number of minor bug fixes.