eSIMs care not a new thing, since companies have been trying to push them for years to cut out the larger nano SIM cards and free up a bit more space inside the phone. But that all depended on networks offering eSIM services, which a lot of them don't. Thankfully O2's getting in on this for a few select phones.
Later this month O2 will be launching eSIM services for the iPhone XS, XR, XS Max, Pixel 3, and Pixel 3 XL. All customers will need to do to swap over is head into their nearest O2 store, or call customer services, to claim an eSIM pack that has everything they need to set the eSIM up.
If O2's pack is anything like EE's it'll look just like a regular SIM card pack you can buy, but uses a QR code to set up the SIM chip that's already inside your phone. Obviously not all phones have an eSIM, which is why the network is being so restrictuve with the phones it's supporting.
O2 also said anyone who wants to use the usual plastic SIM can still do so, so you're not losing out on any sort of choice. But if you want the eSIM, and don't want to be with EE, you don't have very long to wait. The only real question is whether the iPhone 11 and Pixel 4 devices will be supported by O2, since they're expected to arrive pretty soon.