Dubbed “OnePlus Roaming”, this feature has been described as, “OnePlus Roaming lets you surf the internet without a local SIM card. It’s like a virtual sim (only data, no calls); it should work globally in most of the countries/regions, and it will list out the plans available for the country/regions you are in so that you can purchase a suitable plan and access the Internet without a SIM.”
It actually sounds like a pretty cool feature because when you travel and you want to use local internet, you will need to buy a new SIM card. Alternatively you might also have to purchase a roaming plan from your carrier which could be more expensive and less value for money, so this method is more efficient as it will not require you to swap out SIMs.
However as OnePlus notes, this only applies for data so you won’t be able to make regular calls or send SMS, and also because it doesn’t use a physical SIM, it might not necessarily be applicable to all countries you visit, so your mileage may vary.