Traveled for 10 days out of the country with four VZW devices - three iPhone, one Samsung S22. One iPhone had cell radio and roaming turned on, and we expected to get charged (and did) $10 a day. Two other iPhones had cell radio and roaming turned OFF, and yet each was charged $10 a day even though no data, talk, text was used. The Samsung S22 had cell radio and roaming turned off, and was not charged.
Very frustrating to have these different experiences, and attempts to reverse the TravelPass charges on the two iPhones that we didn't use have resulted in endless customer support chats that have gone nowhere.
Airplane Mode, at least for iPhones, appears to be the _only_ way of avoiding TravelPass charges when traveling internationally as a VZW customer. You have been warned!