If you're a public beta tester, your Thursday just got awesome. Apple just released the first public beta for iOS 12.3 today, March 28. This update comes right on the heels of the first developer beta for 12.3, which itself released just one day ago. Thanks to that release, we know that this update contains a new TV app with updated layouts, Apple TV Channels subscriptions, a new logo, and more.
Once you install the update, you'll notice Apple TV Channels is a total upgrade to the TV app, including the ability to pay for and watch subscription services without needing to leave the app. Apple is offering free trials for Showtime, Smithsonian Channel Plus, Starz, and Tastemade through this new service during the initial beta period, with a lot more premium channels lined up for later.
The public beta also likely features bug fixes for issues found in previous versions of iOS, and possibly comes with security patches for any vulnerabilities there might be. We don't know for sure, because the release notes for this software are empty, and because Apple doesn't typically give updated on everything that's changed.
To download and update your iPhone to iOS 12.3 public beta 1, you will first need to be a registered developer with a valid configuration profile. If you have iOS 12's "Automatic Updates" enabled, you can let the software update overnight. To install right away, launch the Settings app, select "General," then "Software Update." Tap "Download and Install," then follow the on-screen prompts.