Any iPhone from the iPhone XS, XS Max and XR onward can keep two lines on standby at the same time. But standby is where "at the same time" ends: mobile data runs on only one line at a time, and while you are on a call you generally cannot take a call to your other number. Most confusion after adding a second line comes from not knowing these rules. Using Apple's own support documentation, this guide covers what you need for two lines, how to set the default line and the data line, what happens to calls on the other line mid-call, and how iPhone decides which number to use for each contact.
A common use is adding a travel eSIM as your second line while keeping your home number. You can pick a plan for your destination from the Coral eSIM plan list.
What you need to use iPhone Dual SIM
According to Apple, Dual SIM is supported on iPhone XS, iPhone XS Max, iPhone XR and later. Which combinations work depends on the model:
- Physical SIM (nano-SIM) plus eSIM: iPhone XS, XS Max, XR and later
- eSIM plus eSIM: iPhone 13 and later
- eSIM only: the iPhone 17 sold in Japan does not support a physical SIM and is activated with an eSIM, so two lines means two eSIMs
An iPhone can store eight or more eSIMs, and two of them can be active at the same time (per Apple's iPhone 17 specifications and support pages). You can keep old travel eSIMs on the phone after a trip, but no more than two lines are ever on standby at once.
Using lines from two different carriers
Apple states that "to use two carriers, your carrier must unlock your iPhone, or both plans must be from the same carrier." If you use an enterprise plan on a company phone, Apple advises checking with your administrator. See how to check whether your phone is unlocked.
iPhone Dual SIM basics: the default line and the data line
When you add a second line, iPhone asks you to decide the role of each one. You can change these later, but knowing what they mean saves a lot of guesswork.
Line labels
Each line can be labeled, for example "Business" and "Personal". You can also type your own name under Settings > Cellular > [the number] > Cellular Plan Label. The label appears in your call history and in Messages, which helps you see which number you are using.
The default line
The default line is the number used when you call or message someone who is not in your Contacts. If you set one line to be used for cellular data only, the other becomes your default.
The cellular data line
iPhone can use only one cellular data network at a time. Choose which line carries data under Settings > Cellular > Cellular Data. Adding a second line does not combine data allowances or let you use both connections at once.
Allow Cellular Data Switching
With this setting on, when you are on a call on the line that is not your data line (the voice-only line), that line automatically switches to handle both voice and data. With it off, cellular data does not work while you are on a call on the voice-only line. Apple also notes that this switching does not work while you are using Data Roaming.
iPhone Dual SIM: calls to your other number while you are on a call
iPhone uses Dual SIM Dual Standby (DSDS), which means both lines can make and receive calls. There are conditions, though, for calls that arrive on your other number while you are already on a call.
- If the other line's carrier supports Wi-Fi Calling, you can answer that call even while on a call
- If your current call is on the line that is not set for cellular data, you also need Allow Cellular Data Switching turned on
- If neither applies, the call goes to voicemail (if you have voicemail set up with that carrier)
- In that case, you won't get a missed-call notification from the other number
If your other line shows "No Service" during a call, it means that carrier does not support Wi-Fi Calling, Wi-Fi Calling is turned off, or Allow Cellular Data Switching is off.
Call Waiting also works only for incoming calls to the same number you are talking on. For a number you cannot afford to miss, Apple suggests forwarding calls from one number to the other. If you are combining work and personal numbers on one phone, think about whether long calls on one line are likely to overlap with urgent calls on the other.
How iPhone Dual SIM picks a number for each contact
The part of Dual SIM that people most often overlook is how the outgoing number is chosen. iPhone does not always call from your default line.
Calls use the number you last used with that contact
Apple explains that iPhone uses the same number you used the last time you called that contact. If you have never called them, it uses your default line. So if you call a client once from your personal number, the next call may go out from that number again.
To fix a number for a contact, open the contact, tap "default" and choose a number. To change the number just before a call, tap the Info button in Favorites, or on the keypad tap the number shown at the top of the screen.
Messages, iMessage and FaceTime
- Messages: after entering a contact in a new message, tap the number shown to choose which one sends it. You can also switch mid-conversation by tapping the number at the top
- iMessage and FaceTime: choose whether to use one number or both
- RCS: available with iOS 18 and later on supported carriers
For receiving verification codes sent to your home number while abroad, see how to get SMS verification codes abroad.
Switching iPhone Dual SIM lines when you travel
The typical travel setup is to keep your home line on standby for calls and SMS, and make a travel eSIM your cellular data line. Everything above applies directly to this setup.
- Use only the travel eSIM for data. Turn Data Roaming off on your home line
- If your travel eSIM uses Data Roaming, Allow Cellular Data Switching will not work, so expect data to stop while you are on a call on your home line
- Apple notes that when Data Roaming is on for your data line, Visual Voicemail and MMS are disabled on the voice-only line
- Per-contact numbers carry over from home. When calling from abroad, check which number is shown before you dial
For step-by-step settings before departure and after arrival, see our Dual SIM travel setup guide. To compare ways of keeping your number, see how to keep your phone number while traveling.
iPhone Dual SIM FAQ
With two lines on my iPhone, can I receive calls on both numbers?
Yes. iPhone Dual SIM lets both lines make and receive calls. While you are on a call on one line, though, a call to your other number goes to voicemail unless that line's carrier supports Wi-Fi Calling, and you won't get a missed-call notification.
How many eSIMs can an iPhone hold?
Apple says an iPhone can store eight or more eSIMs, with two active at the same time. Two eSIMs as two lines works on iPhone 13 and later.
Can I use lines from two different carriers?
Yes, as long as your iPhone is unlocked. If it is carrier-locked, both plans need to come from the same carrier.
Can an iPhone without a physical SIM slot use two lines?
Yes. The iPhone 17 sold in Japan does not support a physical SIM, but with two active eSIMs it works as a two-line phone. Two eSIMs as two lines is supported on iPhone 13 and later.
With two lines, does my iPhone use data on both?
No. Cellular data runs only on the line you choose in Settings. With Allow Cellular Data Switching on, the voice-only line also handles data only while you are on a call on it. This switching does not work during Data Roaming.
Set up iPhone Dual SIM as two lines on standby, not two lines in use
Two lines on an iPhone are useful, but both lines are not always working at the same time. Data runs on one line, a call on one line can cost you calls on the other, and each contact gets whichever number you used last. Keep these three rules in mind, decide your default line, data line and per-contact numbers up front, and both uses work smoothly: separating work and personal numbers, and pairing your home number with a travel eSIM abroad.
For a travel eSIM to use as your second line abroad, choose a plan for your destination from the Coral eSIM plan list.
