[lnl]

See the map on page 7 (PDF page 9) of the GSMA report "Access to Mobile Services and Proof of Identity 2020": https://www.gsma.com/mobilefordevelopment/wp-content/uploads...

To get counts, I also analyzed the table in the annex; it lists exactly 200 countries (checking each of them, that's because in addition to 193 UN members, it includes two non-member countries: Kosovo and Taiwan, and five other non-countries: French Guiana, Greenland, Hong Kong, Macao, Svalbard).

Of these, 34 are listed as "SIM registration not mandated" and further 7 are listed as "SIM registration under consideration", the rest are "SIM registration mandated", i.e. 159 countries.

Basically the whole world requires it except for North America/UK and a few smaller countries mostly in Europe. Also notable that countries without ID requirement mostly happen to be the ones with very low prepaid SIM penetration (see the map on page 6 [page 8 of the PDF]) so their unidentified SIM usage is presumably low anyway, though it remains a possibility in those countries.

Edit: Sorry, 6 are listed as "State of SIM registration inconclusive" which I have missed, so "SIM registration mandated" count should be 153.