In Europe, I usually use the O2 Europe travel esim from esim.net. 48 countries, 20gb for $20 USD, 35gb for $23, includes +44 phone number with free local in-country calls for each of the 48 countries (i.e. when in Italy you can call Italian numbers for free and the same with the other countries). Biggest limitation is you can't send SMS except in UK. You can receive them in all 48 countries.

NOTE: the 30 days start the moment you buy the plan (based on whatever day it is in the UK). So I normally buy it at time of departure to Europe.


Coverage in 48 countries, Austria, Azores, Belgium, Bulgaria, Canary Islands, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, French Guiana, Germany, Gibraltar, Greece, Guadeloupe, Guernsey, Hungary, Iceland, Ireland, Isle of Man, Italy, Jersey, Latvia, Liechtenstein, Lithuania, Luxembourg, Madeira, Malta, Martinique, Mayotte, Monaco, Netherlands, Norway, Poland, Portugal, Reunion, Romania, Saint Martin, San Marino, Slovakia, Slovenia, Spain, Sweden, Switzerland, United Kingdom and Vatican City.

https://www.esim.net/o2/travelplus