Use Dual SIM iPhone with Apple Watch cellular models
If you set up multiple cellular plans using Dual SIM on your iPhone XS, iPhone XS Max, or iPhone XR, you can add multiple lines to your Apple Watch with cellular, then choose the one your watch uses when it connects to cellular networks.
Note: Each iPhone cellular plan must be provided by a supported carrier and must support Apple Watch cellular.
Set up multiple carrier plans
You can add one plan when you set up your watch for the first time. You can set up a second plan later in the Apple Watch app by following these steps:
Open the Apple Watch app on your iPhone.
Tap My Watch, then tap Cellular.
Tap Set Up Cellular or Add a New Plan, then follow the steps to choose the plan you want to add to your Apple Watch.
You can add multiple lines to your Apple Watch, but your Apple Watch can connect to only one line at a time.
Switch between plans
Open the Settings app
on your Apple Watch.Tap Cellular, then choose the plan you want your watch to use.
You can also open the Apple Watch app on your iPhone, tap My Watch, then tap Cellular. Your plan should automatically switch. If it doesn’t switch, tap the plan you want to use.
How Apple Watch receives calls when using multiple cellular plans
When Apple Watch is connected to your iPhone: You can receive calls from both lines. Your watch shows a badge that tells you which cellular line you received a notification from—H for Home, and W for Work, for example. If you respond to a call, your watch automatically responds from the line that received the call.
When Apple Watch is connected to cellular and your iPhone isn’t nearby: You receive calls from the line you’ve chosen in the Apple Watch app. If you respond to a call, your watch automatically calls back from the line you’ve chosen in the Apple Watch app.
Note: If the line you’ve chosen in the Apple Watch app isnʼt available when you try to return a call, your watch asks if you want to respond from another available line that you've added.
How Apple Watch receives messages when using multiple plans
When Apple Watch is connected to your iPhone: You can get messages from both plans. If you respond to a message, your watch automatically responds from the line that received the message.
When your Apple Watch is connected to cellular and away from your iPhone: You can get SMS messages from your active plan. If you respond to an SMS message, your Apple Watch automatically texts back from the line that received the message.
When your Apple Watch is connected to cellular or Wi-Fi and your iPhone is turned off: You can send and receive iMessage texts as long as your Apple Watch has an active data connection to a Wi-Fi or cellular network.
For more information about Dual SIM and iPhone, see the Apple Support article Use Dual SIM with Apple Watch Series 4 (GPS + Cellular) and Apple Watch Series 3 (GPS + Cellular) and iPhone User Guide.