They are selling local data-plans abroad without switching the SIM card by implementing RSP. Calls are coming in 2017, also promising a portable phone number later that year.
See picture of the process here: https://twitter.com/lathiat/status/758979125751054336
Works fantastically and gives me $30/GB data in pretty much any country at often 4G speeds - with a 12 month expiry on the data (does cost $20 a year or something for 'membership' but still, usually costs far more than that for a sim starter pack in every different separate country you go to). Good for frequent travellers!
Obligatory please use my referral link if you signup :-) Bonus 100MB for both me and you. http://www.flexiroamx.com/referYXBBCJ / Code YXBBCJ
Some European operators still have cheaper roaming data plans
In the case of a true eSIM, there is no sim card at all, it's stored on the device it's self with a lower level bootstraping profile (i.e. not an alternative pre-programmed carrier)