Is San Marino included in most "Europe" or "UK" roaming plans?

Almost never. Because San Marino is not in the EU, most international carriers (especially from the UK, USA, or Canada) exclude it from their standard "Europe" packages, placing it in the same high-cost category as Monaco or Switzerland. You must check your home plan's fine print. A eSIM Scout eSIM is the only way to guarantee a fixed, prepaid data price.