OnePlus Switch application is finally made available for OnePlus smartphone users on Google Play Store. With the OnePlus Switch application, users can easily transfer files from their previous device to the new OnePlus smartphone. At the moment, the OnePlus Switch application has the ability to transfer contacts, messages, call logs, calendar, photos, videos, audio, applications (without data). It's understandable that the application can not transfer application data from one phone to another.
That said, you can receive data from any of your previous Android/OnePlus devices to your new OnePlus device. And you can only send data from your OnePlus device to a new OnePlus device, and not a new Android device.
Back at the launch event of the OnePlus 5T in New York City, OnePlus said that it would be releasing the OnePlus Switch application anytime soon, solving the woes of OnePlus users migrating from an old OnePlus device to a new OnePlus device. Sadly, the OnePlus Switch application at the moment is limited only to Android users. If you're coming from an Apple iPhone to any OnePlus device, then you're out of luck.
This application can be installed on any Android device running Android 5.0 Lollipop and above, but like I stated, a OnePlus device is required to send/receive the data. Also, the app is in beta stage at the moment, and a stable version will be released sometime in mid-January.
This is a nice move from OnePlus as the company is allowing its users who're upgrading their smartphones by not losing any data. Google already has an auto-backup service integrated into every Android smartphone, but it just keeps the app data and prompts you while setting up a new Android smartphone whether to restore the data or not. Thankfully, with some apps, Google also backs up app data, only if the application has support for it.
That said, if you own a Google Pixel smartphone, then you're lucky enough as Google's auto-backup service works even for call history, launcher settings, SMS messages, local contacts/calendar (standard sync though), and photos/videos (thanks to Google Photos app). But at the moment, this feature is limited only to Google Pixel smartphones.