European Union Roaming rules
Indeed since 2017 June 15 the European Union’s directive says mobile carriers cannot charge any extra to use your phone in European Union than they would for you to use it in your ‘EU home’ country, as the rule “Roam Like Home” suggests, this ensures you won’t suffer from bill shock – unexpected and significantly larger - than normal mobile phone bills when traveling.
The new European Union rules apply beyond the European Union, 'free' roaming does apply to all 28 EU countries. it was also extended to Liechtenstein, Iceland and Norway (the three additional countries in the European Economic Area, if you like jargon) thanks to an agreement between the European Union and the EEA countries.
Menzies: «they were no longer roaming while traveling Europe» «So I believe you will be fine»
GFC's question was about Switzerland, Germany and France .
Switzerland is geographically in Western Europe however is not a member state of the European Union neither EAA althought Switzerland is a member of the Schengen Area. Swiss have a long tradition of neutrality.
Therefore the new European Union rule “Roam Like Home” does not apply to Switzerland. Most of European Union phone users are still subject to roaming charges when they are in Switzerland.
Menzies: «BTW, the supermarket chain Tescos sells sim cards and data/voice plans as well»
Tesco is a British multinational groceries and general merchandise which operates in UK and Poland, not in Switzerland, France and Germany. The French company Tesco, the homonym of the British one, is a holding financial company which does not have operating assets in France, Germany and Switzerland.
GFC: «Anyone have experience in this? Anyone who lives in those countries have any advice on how to make this work?»
My advice is to bring an extra cellphone unlocked by your US network then to buy a pay-as-you-go SIM card in Strasbourg, France - your first stop in European Union coming from Basel, Switzerland - which you can use in France also Germany and Luxembourg according to the European Union free roaming. This is probably the best option. Before leaving the US just check to make sure your extra phone is unlocked.
As an example French telecom company ORANGE is proposing:
A SIM card «*Orange Holiday*» with a French phone number, 120 min + 1000 texts, international calls and texts from European zone to worldwide, unlimited free incoming calls from worldwide, 10GB of mobile data valid in European zone (Switzerland included). Euros 39, validity of the credit : 14 days after 1st use.
Also with the combination of the 10 GO Internet data and a free app as WhatsApp, Telegram or Signal, you can receive, call, talk and txt unlimited for free over the Internet both ways with your contacts in the US. You'll just need to make sure that your contacts have the same app installed on their phone. If they do, they will automatically appear.
Bon voyage