Managing your iPhone's dual-SIM feature can be confusing, especially when it comes to choosing which SIM card uses mobile data. This guide will walk you through the steps clearly and simply, along with some useful tips and answers to common questions.

 

 Step-by-Step Setup

Open Settings: Tap on "Cellular" (iOS 14 and later) or "Mobile Data" (older versions).

Select Default Data SIM:

Tap "Cellular Data".

Choose the SIM card (SIM 1 or SIM 2) you want to use for mobile data.

Set Default Calling SIM (Optional):

Tap "Default Voice Line".

Pick the SIM you usually use for calls.

 

Advanced Settings

Situation	What to Do
Switch Data SIM Temporarily	Go to "Cellular Data" and manually choose the other SIM.
Use a Specific SIM for an App	In "Cellular", select an app and then choose which SIM it should use.
Turn Off Data for the Secondary SIM	In "Cellular", go to the secondary SIM settings and toggle off "Cellular Data".

 

Things to Remember

⚠️ Dual-SIM Limitations

When both SIMs are active, some models may switch to 4G.

For international travel, turn on "Data Roaming" in "Cellular" → "Cellular Data Options".

⚠️ Signal Priority

If the main SIM has a weak signal, it won't switch to the secondary SIM's data automatically. You must change it manually in "Cellular Data".

 

Frequently Asked Questions

Q: Can't access the internet after setting?

→ Check your APN settings (usually, your carrier configures this automatically).

→ Restart your iPhone or remove and reinsert the SIM cards.

Q: How can I tell which is the main or secondary SIM?

→ Customize labels at the top of "Cellular" (e.g., "Main - Work" or "Secondary - Personal").

Q: Does it support dual 5G?

→ Only iPhone 12 and newer models support dual 5G, but your carrier must offer 5G services too.

 

After Setting Up

You'll see the current data SIM's signal in the status bar (e.g., "Main SIM shows 5G, Secondary SIM shows LTE"). It's best to set your frequently used SIM as the default to avoid unexpected data charges. Happy browsing! 📶