Short answer: use 4S eSIM for mobile data and prevent your primary SIM from using roaming data.
Recommended setup
- Select the 4S eSIM label as mobile data.
- Turn on data roaming for the 4S eSIM line.
- Turn off data roaming for your primary SIM.
- Disable automatic mobile data switching if your phone has that option.
Your primary carrier may still charge for calls, SMS, voicemail, or roaming services.
Need help?
Contact 4S support through support@4s.net, a Zendesk support ticket, or Zendesk live chat. Do not reply to hi@4s.net; it is an automatic order and installation email sender.
When contacting support, include your order email, ICCID if available, destination, phone model, and screenshots of the error or SIM/eSIM settings page.