Modern smartphones are almost always equipped with slots for two SIM cards, which allows users to separate personal and work communications or use tariffs from different operators to save money. However, this convenient feature often becomes a source of confusion when you need to make an urgent call. The default Android system may try to guess your intent or always use the same card, which is not always convenient.
In this article, we will take a closer look at how to control the choice of telecom operator directly at the time of dialing, as well as how to set global priorities so that your phone behaves predictably. We will look at the settings in pure Androidas well as the features of interfaces from Samsung, Xiaomi and other manufacturers, since the operating logic may differ.
Understanding how the mechanism call routing works in your system will help you avoid unnecessary expenses for roaming or calls from a card that has run out of minutes. Let's move from theory to practice in setting up your device.
Global default SIM selection settings
Before understanding the choice of card for each specific call, you need to understand how the basic setup works. In most versions of Android, there is a setting that controls how the system behaves in the absence of explicit user input. If you haven't changed these settings, the phone is likely using one card for everything or asking you every time.
To change this behavior, you need to go to the settings section, which is usually called Connections or Network and Internet. Here you will find the item SIM card manager or SIM card settings. This is where you set default card for voice calls and mobile data.
There are three main operating modes that you can select:
- 📱 Always ask: every time you dial a number or click on a contact, the system will show a pop-up window with the choice of SIM 1 or SIM 2.
- 🔒 Fixed SIM 1: all outgoing calls will go through only the first card, ignoring the second, until you change the setting manually.
- 🔐 Fixed SIM 2: similar to the first option, but priority is given to the second card, which is convenient if it has unlimited minutes.
⚠️ Attention: If If you select the “Always Ask” mode, be prepared for the fact that when dialing emergency numbers or using speed dial widgets, the system may not have time to show the choice if the interface freezes. For the reliability of critical calls, it is better to install a fixed card.
Changing these parameters does not require rebooting the device and takes effect instantly. However, it is worth remembering that some older phone models or specific firmware may not support real-time dynamic switching without briefly interrupting registration in the network.
Selecting an operator at the time of making a call
Even if you have a default card installed, the situation often requires flexibility. For example, you need to call a colleague using a work SIM card, although your home SIM card is configured for personal calls. In modern Android shells, this process is implemented intuitively, but has its own nuances depending on the dialing method.
When manually dialing a number via standard dialer, after entering the numbers, but before pressing the green handset, you will see the currently selected card. It is usually displayed with a small operator icon or SIM name below the input field. Clicking on this icon instantly switches the active line to another.
If you are calling from your contact list or call history, the logic may be different. In pure Android clicking on a contact name, the call goes straight through the default card. To select another, you need to either hold your finger on the call button (in some launchers), or first open the contact card and click on a specific phone number, where a choice is sometimes offered.
Owners of smartphones Xiaomi (MIUI) and Huawei (EMUI) are luckier: these shells often implement double pressing. The first press of the call button in contacts does not initiate a call, but opens the SIM selection menu if the appropriate mode is configured. This prevents accidental calls from the wrong card.
If you often forget to change the card before making a call, turn on the sound alert in the dialer settings. Many phones can announce the name of the selected SIM before connecting.
It is important to note that when switching cards, the number is not reset while dialing. You can enter a long number, see that the wrong SIM is selected, switch it and press call - all numbers will be saved in the input field.
Features of interfaces of Samsung, Xiaomi and other brands
Smartphone manufacturers often modify the standard Android code by adding their own Dual SIM control functions. This can both simplify and complicate the life of a user who is accustomed to the logic of pure Google Pixel.
In devices Samsung Galaxy with a shell One UI control is placed in a very clear menu. When calling from contacts, if the setting is “Always ask”, a beautiful pop-up window appears with large SIM 1 and SIM 2 buttons. There is also a checkbox “Remember the choice for this contact”, which is a unique and extremely useful function.
Smartphones Xiaomi and Redmi allow you to flexibly customize the behavior for different types of rooms. You can set a rule: calls to landline numbers go through SIM 1, and calls to mobile numbers through SIM 2. This setting is in the deep menu Settings → SIM cards and mobile networks → Advanced.
Below is a table comparing SIM selection options in popular shells:
| Shell / Brand | Select when calling from contacts | Remember selection | Voice notification |
|---|---|---|---|
| Pure Android (Pixel) | Via call menu | No (global only) | Depends on version |
| Samsung One UI | Pop-up window | Yes, for each contact | Yes |
| Xiaomi MIUI | Pop-up window / Hold | Yes | Yes |
| Realme UI | Pop-up window | Yes | Optional |
Users Honor i Huawei it is worth paying attention to the "Smart SIM selection" function. The phone can analyze call history and suggest the card with which you most often called this subscriber previously, even if the global setting is different.
Samsung secret function
In Samsung phones, you can set different melodies for SIM 1 and SIM 2. When you receive a call, you immediately hear which line the call is on, which helps you quickly decide which card to answer or call back.
Automatic SIM selection based on contacts
One of the most convenient functions for owners of two SIM cards is the ability to link a specific phone number to a specific SIM card. This eliminates the need to manually select an operator each time when calling regular subscribers.
The implementation of this feature depends on the Contacts application you are using. In the standard Google application, the process is as follows: you open a contact card, click on the three dots in the corner of the menu and select SIM settings or Always use this SIM. After this, the system remembers your choice.
Unfortunately, this function does not work in all versions of Android and not in all phone books. If you do not find such a setting in the contact card, try the following workaround: make a call to this person from the desired SIM card. Some smart phone algorithms will automatically remember this choice for future calls.
For business users, this is a critical setting. It allows you to avoid situations when a confidential conversation accidentally goes through a personal SIM card, or vice versa, a personal call is charged as a work call.
⚠️ Attention: The SIM memory function for a contact can be reset after clearing the data of the "Phone" or "Contacts" application, as well as after resetting the network settings. Be prepared to reconfigure priorities for important subscribers after such procedures.
If your phone does not support system-level binding, you can use a trick: save the same contact twice with different names, for example “Boss (Work)” and “Boss (Personal)”, and link them to different quick sets or simply use different entries for different purposes.
Solving problems with SIM selection and switching
Sometimes users are faced with a situation where the phone ignores settings, does not show the selection menu, or switches SIM cards chaotically. Most often this is due to software failures in the communication module or a settings conflict.
First, check whether both SIM cards are active physically and software. Go to Settings → Connections → SIM card manager and make sure that the switches opposite both cards are in position Enabled. If one of the cards is disabled, the phone will not be able to offer it for selection.
The second common reason is outdated software. Manufacturers often release patches that correct the logic of Dual SIM operation. Check for updates in the section Settings → About phone → Software update.
If the problem persists, try resetting the network settings. This won't delete your photos or apps, but it will reset your Wi-Fi, Bluetooth, and mobile network settings to factory defaults. The path to this function usually looks like this: Settings → System → Reset → Reset Wi-Fi, mobile data and Bluetooth settings.
☑️ Diagnosis of problems with SIM
In rare cases, the problem may be in the card slot itself or in the adapter if you are using an adapter from nano-SIM to micro-SIM. Try swapping the cards: insert SIM 1 into slot 2 and vice versa. If the problem “moved” with the card, the problem is in it or in the operator.
The influence of 5G and VoLTE mode on the choice of SIM card
With the development of fifth generation networks (5G) and voice communication technology via LTE (VoLTE), the architecture of two SIM cards has become more complicated. In some configurations, when there is an active conversation on one SIM, the second one may temporarily lose registration in the network or switch to 2G/3G mode.
This is important to consider when choosing a card for a call. If you're in a 5G coverage area and have two active cards, your phone may limit internet bandwidth on the second card while you're calling on the first. This does not affect the choice of SIM card for a call, but it does affect the quality of communication in parallel.
Some operators require VoLTE to be enabled for stable operation of two SIM cards simultaneously. If you notice that when making a call from one card, the second one becomes unavailable (“subscriber unavailable”), check the VoLTE settings in the mobile networks menu for both profiles.
⚠️ Attention: 5G and VoLTE network settings depend on support from your telecom operator. Even if the phone supports these functions, the operator may block them or require additional activation of the service in your personal account.
It is also worth considering that in Dual SIM Dual Standby (DSDS) mode, which is used in 99% of modern smartphones, there is physically one radio module, but it quickly switches between two networks. Under intense load (for example, downloading a file on one SIM and making a call on the other), delays may occur in network selection.
DSDS technology allows you to keep both SIM cards in active standby mode, but only one of them can physically receive data or voice at a particular time, unless Dual Active mode is used.
Frequently asked questions (FAQ)
Is it possible to set different ringtones for different SIM cards?
Yes, this is possible in most modern Android smartphones. Go to the settings of the "Phone" or "Sound" application, find the "SIM Card Ringtones" section and assign unique ringtones for incoming calls to the first and second line. This will help you understand which card they are calling you on without looking at the screen.
Why does the phone itself switch the SIM card during a call?
You most likely have Switch Data During a Call or a similar smart control option enabled. In some cases, if the primary SIM network loses signal during a call, the phone may try to transfer the call to the second card (if call transfer technology is supported), but more often this is simply a network registration failure.
What to do if the SIM selection icon disappears during a call?
Check the global settings in the "SIM Card Manager" section. Perhaps the "Always use SIM 1" mode was accidentally selected there. Change the setting to "Always ask" or "Preferred SIM" and the selection menu should return.
Does the choice of SIM card affect the quality of communication?
Indirectly - yes. The quality of communication depends on which operator has better reception in a given area. If you forcefully select a SIM operator with poor coverage in a specific location, the quality will be poor. Use widgets or settings to manually select an operator with the best signal when roaming or outside the city.
Is it possible to block calls from a specific SIM card?
There is no direct ban, but you can disable the second SIM card in the settings if you want to be guaranteed to make calls from only one. Or use parental control applications or third-party dialers that allow you to block outgoing calls from selected numbers.