Is roaming free in Switzerland with my EU/UK/US SIM card?

No! This is the most common mistake. Although Switzerland is in the Schengen Area, it is NOT a member of the European Union (EU). Therefore, the EU's "Roam Like at Home" policy does not apply. Most EU and UK carriers (like Vodafone, O2, T-Mobile DE) will charge you expensive international roaming fees. For US travelers, it's a high-cost "Day Pass." A Cellesim eSIM is a one-time prepaid fee that is significantly cheaper.