In addition to your physical SIM card, you can add eSims to your smartphone by scanning a QR code. eSims connect to a mobile network, just like regular SIM cards. You can buy an eSIM online and start using it immediately. [Airalo](http://airalo.com/) makes it easy to purchase data eSIMs for any country. The steps are: 1. Install the app, tap a few buttons. 2. Pay with Google/Apple Pay. 3. Scan the QR code. 5G connections speeds are often available. The prices are usually reasonable: similar or cheaper than other short-term data SIM options, especially in the USA. N.B. In some countries, local providers offer better prepaid eSim deals that are easy to buy and activate online. For example: in Iceland you can get 100 GB from nova.is for $36, while Airalo only gives you 20GB for the same price. I've used Airalo in the USA, Iceland, Portugal and Germany. It's great!