eSIM

A SIM built into your phone that you activate by downloading a profile, with no physical card to insert.

The practical advantage for travellers is that you can buy and install one before you fly, so you land already connected and skip the airport queue. The practical limitation is that it is tied to the device you install it on and generally cannot be moved to another phone.

Your phone must support eSIM and must be carrier-unlocked. Most iPhones from the XS onward and recent Android flagships qualify; many mid-range and older handsets do not.