Xiaomi’s current smartphones, which run on the shell of MIUI or HyperOS, are designed to meet the needs of users who need to manage multiple numbers, such as separating personal and work calls, using different tariffs to save on communications, or having a backup channel in areas with unstable coverage. Unlike many Western brands, Chinese manufacturers have long implemented full support for Dual SIM as a de facto standard for all their devices, from budget Redmi to flagship series.
The process of physical installation and software activation of cards is usually easy, but in the Android operating system with a proprietary add-on, there are many subtleties: they relate to traffic distribution, setting up voice calls over different networks and optimizing power consumption. The correct configuration avoids situations where the phone “loses” the network or incorrectly determines the priority SIM card for Internet access. It is important to understand that simultaneous operation of two cards in 4G/5G mode is possible only on models that support Dual 4G VoLTE technology.
In this article, we will discuss in detail all the stages of setting up, from installing a tray to finely adjusting network parameters. You will learn how to make your smartphone use the fast Internet of one card, saving voice communication on another, and what to do if the device does not see the second module.
Preparation for installation and compatibility check
Before you start the software setup, you need to make sure that the device and the SIM cards themselves are physically ready. Modern Xiaomi smartphones use combined trays that can be made in the format of "two nano-SIM" or "nano-SIM + microSD." Carefully examine the end of the case: if the tray has two notches on one side or two separate sites, your device supports two numbers at the same time. If the tray has space for only one card and a memory card, you can activate the second number without cutting the SIM card or using adapters.
Also worth paying attention to is the age of your SIM cards: Older hand-cut Mini-SIM or Micro-SIM cards can incorrectly contact the current collectors of a new smartphone, often resulting in read errors or no signal at all. Operators are replacing old cards with new nano-formats for free, which is the most reliable solution. PIN-code, or know it in advance, as the Android system will request it immediately after turning on the phone.
⚠️ Warning: Never try to insert a tray into a smartphone unless the cards are stacked perfectly evenly in it.Mechanical pressure can damage the contacts inside the slot, leading to costly motherboard repairs.
To check the compatibility of frequencies and technologies, you can use built-in diagnostic tools. Enter the phone app code ##4636## to get to the engineering menu. Here, under Phone Information, you can see the status of each SIM card and supported network types. This is especially useful if you plan to use cards from different carriers, as their frequency ranges may differ.
Physical installation SIM-card-tray
The installation process begins with the removal of the tray. This uses a special clip that comes with the kit, or a thin needle. The extraction hole is usually located on the lower end of the device, next to the USB-C charging port, or on the upper end depending on the model (Redmi Note, Poco, Mi).
Put the SIM cards in the appropriate recesses. On most modern Xiaomi models, the tray is bilateral or has a special bevelled shape that prevents improper installation. The bevelled corner of the card should coincide with the bevelled angle in the tray. If you use a hybrid slot and you need a second SIM card, you will not be able to install the microSD card, you will have to choose between an additional number and a memory extension.
☑️ Pre-insertion check
Once installed, gently press the tray back into the case until it is fixed. Don't put too much effort; if the tray doesn't enter easily, check the orientation of the cards. Turn on the smartphone. If you install the cards on the device on (hot replacement), the system may not immediately recognize them, so a full reboot is recommended. The screen will light up, and after a few seconds two signal icons should appear in the status bar, indicating successful physical activation.
Initial network setup and operator selection
After booting the Android operating system with a shell MIUI, The device will automatically attempt to log in to the networks of available carriers. If the SIM cards are new or have not been used in this region before, you may need to manually configure the access points (APN). Usually the necessary parameters are loaded automatically through SMS-If this doesn't happen and the Internet doesn't work, you'll have to manually enter the data.
To set up, go to the Settings menu → SIM-Maps and mobile networks. Select the SIM card you want (SIM 1 SIM (2) and click on “Access points (APN)". You need to create a new point by entering the data provided by your carrier (usually this is the name of the point and the address, for example, the Internet for many operators.
In the same menu section, it is important to set up your preferred network type. For each SIM card, you can choose the mode of operation: 2G/3G/4G (auto), only 4G or only 3G. It is recommended to leave automatic mode for better compatibility. However, if you are in the zone of weak signal, forced switching to 3G can stabilize voice communication, although the speed of the Internet will drop.
⚠️ Note: When selecting the "Only" mode 4G" or "Only." 5G" You may lose the ability to receive incoming voice calls if your carrier or phone does not support VoLTE (Voice over) technology. LTE). The phone will be invisible to the caller.
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If the Internet doesn't work automatically, try turning on and off Aviation Mode, which will force the device to re-register on the network with the updated settings.
Distribution of functions: calls and mobile Internet
One of the key features of the system is the flexible distribution of roles between SIM cards, so you can assign one card to the mobile Internet, and use the other only for calls and calls. SMS, Or you can set the switch depending on the situation. → SIM-Maps and mobile networks have a "Default" section, where you set the parameters for mobile data, calls and messages.
Mobile Data defines which channel to access the Internet. This is a critical parameter, since the second SIM card in standby mode can only work in 2G/3G mode to save energy if the phone does not support a full Dual 4G. So it is logical to assign a data card to one that has a tariff with a large amount of traffic or higher speed in your area.
For voice calls, the system offers three options: always use SIM 1, always use SIM 2, or ask every time you call. The latter option is convenient if you make frequent international calls or call numbers inside the network of one of the operators to save money. When dialing, a pop-up with a selection of a SIM card will appear on the screen.
Below is a table showing recommended settings for different use cases:
| Use case scenario | Map for the Internet | Call card. | Recommendation |
|---|---|---|---|
| Working and personal | Personal (no limit) | Ask every time. | Monitoring of expenditures |
| Main and reserve | Main (4G) | Basic | Stability of communications |
| roaming | Local SIM | Local SIM | Saving money |
| Two networks (coverage) | Operator A (where is 4G better) | Operator B (where voice is best) | Maximum signal |
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The correct distribution of roles between SIM cards allows you to extend the battery life of the smartphone up to 20% by disabling 4G modules on the second, less priority card.
Configure the display of contacts and names
When using two numbers, you have to organize your address book. Xiaomi defaults to save your contacts in your Google account or on your device, making them available for both numbers. However, if you want to divide the threads rigidly, you can use the caller name display feature.
Each SIM card has a "Must display the name of the caller" option, which allows you to match the contacts from the phone book to a specific number, which is especially useful when the same person can call you on different numbers (for example, from work and personal), the system will highlight which line the call is coming to, which helps you quickly decide on the answer.
Also worth paying attention to the settings for blocking unwanted calls. Antispam in MIUI works independently for each SIM card. You can set the blacklist or Do Not Disturb mode individually. For example, the working SIM card can be switched to quiet mode on weekends, while the personal one will work normally.
How do I hide the number when I call?
Problem Solving and Diagnostics
Despite the fact that the processes are fine, users may encounter a number of problems, the most common being “No Network” or “Only Emergency Calls” on one of the cards. Often this is solved by resetting network settings. To do this, go to Settings → Connection and Sharing → Reset Wi-Fi, mobile network and Bluetooth. Note that this action will delete saved passwords from Wi-Fi and associated Bluetooth devices, but will not affect your personal files.
Another common problem is the inability to enable 4G on the second SIM card. As mentioned earlier, this is a hardware or firmware limitation. In some regions (European versions), Dual 4G support may be software limited. Check for system updates in Settings → About Phone, as newer versions of MIUI often contain patches for modems.
If your phone is constantly losing signal or switching between 3G and 4G, try manually selecting a network operator. In the network selection menu, turn off the automatic mode and wait for the search to end. Select your carrier from the list. This helps to lock the connection to a particular tower if there is interference from neighboring frequencies in the area.
⚠️ Note: If after resetting the network settings and flashing the phone continues not to see one of the SIM cards, the problem may be hardware.
☑️ Actions if the signal is missing
The Impact of Two SIMs on Autonomy and Performance
The use of two active SIM cards inevitably affects battery life. The second radio, even when in standby mode, consumes energy to maintain registration on the network and search for a signal. In low coverage (outside the city, in basements), energy consumption can increase by 15-25%, as the phone has to constantly amplify the signal.
In addition, active data exchange on one card can create micro-breaks of communication on the second, if the device is not equipped with an advanced modem with DSDS technology (Dual SIM Dual Standby). In games or watching videos, this is usually not noticeable, but when downloading heavy files, short-term delays (pins) in online games are possible if the second number receives an incoming call.
To optimize nighttime or in areas where only one operator catches, you can temporarily turn off the second SIM card programmatically. In the SIM control menu, you just need to switch the switch to off. This will completely turn off the radio module of the second card, keeping the battery charge, but leaving the first number active for important calls.