Owners of Xiaomi Mi 9T smartphone often face the need to use two SIM cards at the same time, whether it is the separation of work and personal contacts or the use of advantageous tariffs of different operators. This model, despite its age, remains popular due to the quality screen and performance, but the MIUI interface can confuse beginners when setting up the connection. The correct configuration of slots and software switches will allow you to effectively manage incoming calls and mobile traffic without constantly removing the tray.
The second-line activation process does not require complex technical knowledge or root rights, but has its own nuances depending on the firmware version. The Android system in the shell of MIUI provides flexible tools for assigning tasks between SIM cards. In this article, we will discuss in detail the physical aspects of installing the card, software setting priorities and solving typical problems that can be encountered during the operation of the device.
Before you start software settings, you need to make sure that the physical installation of the communication module is correct. The sim card tray in Xiaomi Mi 9T is located on the lower end of the case and is combined with a memory card slot, which requires accuracy when extracting. Use a special clip from the delivery kit to avoid damaging the latch mechanism, and carefully examine the contacts for contamination.
⚠️ Attention: Before removing the tray of the SIM card, be sure to turn off the smartphone. While current standards allow hot replacement, in devices with a hybrid slot and a specific Qualcomm Snapdragon architecture, this can result in a short-term network glitch or damage to the card file system.
The second SIM card is installed in either of the two tray positions, since both slots support the Nano-SIM standard. Xiaomi Mi 9T design allows you to use two nano SIM cards at the same time, but this eliminates the possibility of installing a microSD card if you decide to use both slots for communication. Once installed and turned on, the system automatically recognizes the new modules and offers a basic setup.
The initial activation occurs immediately after the smartphone is turned on, when the system setting window appears on the screen. SIM-The operating system will ask you to assign profile names, such as "Main" and "Working", or use carrier names for easy identification.
If the automatic window doesn't appear, you'll need to go to manual configuration mode via the main menu of the device. To do this, open Settings and find the section responsible for wireless networks and connections. MIUI, this paragraph may be called"SIM-Maps and mobile networks" or have a similar name in the "Connections and Sharing group".
Inside the SIM control menu, you'll see a list of profiles that have been set with activity switches. Make sure the switches opposite both numbers are activated and lit in blue or green. This is where the second line is activated, without which the phone won't register on the second operator's network.
Once both profiles are enabled, the system will suggest customizing the use cases for each, a critical step in determining which SIM card will be responsible for voice and which will be responsible for data, and misallocating roles can lead to unexpected Internet costs or missed important calls if the primary number is occupied or out of reach.
In the default settings block, you can choose the priority SIM card for voice calls. The Xiaomi Mi 9T logic allows you to set a permanent profile for all outgoings or request a choice every time you call. The second option is more flexible, but requires extra action when dialing, while the first provides instant dialing according to the usual scenario.
☑️ Setting communication priorities
Special attention should be paid to setting up mobile Internet. In most cases, the second line is used as an additional source of traffic or a backup channel. Select the SIM card in the "Mobile Internet" option on which you have the most profitable tariff plan or unlimited data package.
For users who travel frequently or use corporate communications, the “Use second SIM for calls when the first one is not available” feature is useful. This option allows you to avoid missing important calls when the main number is out of network coverage or overloaded. Activating this feature increases the reliability of communication, but requires that both numbers are active and have a positive balance.
| Setup parameter | Recommended value | Impact on work |
|---|---|---|
| Voice calls | Always ask / Main / Main | Control of communication costs |
| Mobile Internet | Map with unlimited traffic | Speed and money saving |
| SMS-message | The basic SIM card. | Receipt of confirmation codes |
| 4G/5G Preferences | Included for the main | Stability of connection |
Modern smartphones, including the Xiaomi Mi 9T, support VoLTE technology, which allows voice calls over fourth-generation networks.This provides high sound quality and the ability to use the Internet and voice simultaneously without switching to 3G or 2G. Activating this feature is especially important if you use one of the SIM cards for Wi-Fi distribution or navigation during a conversation.
To enable VoLTE, you need to go to advanced mobile network settings. Find the option "Use VoLTE" or "Calls over LTE" and activate it for both profiles if your operator supports this technology. The visual indicator of successful activation is the HD or VoLTE icon in the status bar next to the signal level.
What to do if VoLTE is not working?
In some regions or operators, settings for the APN access point for the second SIM card may not apply automatically, which leads to a situation where the SIM card is visible on the system, but the Internet through it does not work, in which case manual creation or editing of the access point profile is required.
Go to the SIM card selection menu for the Internet, click on the operator name and select "APN" where you can create a new profile by entering the data provided by your carrier. Usually, just enter the APN name, the remaining fields are filled in automatically by the system or remain empty.
Name: MTS Internet
APN: internet.mts.ru
User name: mts
Password: mts
Type APN: default,suplOnce you save the settings, be sure to restart your smartphone or turn on and off flight mode. This action will force the modem to restart and apply new registration options on the network. If the Internet is working but is unstable, try changing the network type in your preferred mode to "LTE Only" to check the signal quality.
⚠️ Note: When manually entering settings APN Keep the letter register and no spaces. One mistake in writing the address of the access point, for example, Internet.mts.ru with a space at the end, will lead to complete inoperability of the mobile Internet on this SIM card.
Managing two numbers is much more convenient when using built-in MIUI features, so you can customize different tunes for each SIM card to understand which number the call was made to without looking at the screen, and this is implemented through a standard call menuer, where each profile is selected for its own audio file.
Also useful is the default limiting feature: You can set a ban on making calls from the second SIM card, leaving it only for receiving calls and SMS. This will prevent accidental spending if the second card is used rarely or has a high tariff per minute of conversation.
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Use desktop widgets to quickly switch your SIM card for the internet, which is more convenient than going into the deep menu settings every time.
Despite the system's fine-tuning, users sometimes run into problems when the second line stops being defined or loses the network, often due to a software failure in the radio unit or a configuration conflict after a system update. The first step should always be to reboot the device, which solves most temporary glitches.
If the reboot didn’t work, try to remove the SIM card and check it on another phone, which will prevent the physical malfunction of the communication module itself or damage to contacts. In case the card is running on another device, the problem may lie in the Xiaomi Mi 9T software.
In complex cases, resetting your network settings to factory values helps, and this operation will not delete your personal data, photos or contacts, but will return all your connection settings, Bluetooth and Wi-Fi to their original state, and you can find this option in Connections and Sharing -> Reset Wi-Fi, Mobile Networks and Bluetooth.
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Resetting network settings is a safe and effective way to eliminate registration errors of the second SIM card without losing personal data of the user.
Energy consumption is an important aspect when using two active SIM cards. Constant network search, especially if one of the operators has weak coverage in your area, can significantly drain the battery. Android is optimized for Dual SIM mode, but the physics of radio waves requires energy to maintain communication with two towers at the same time.
To save charge, you can turn off the second SIM card overnight or during periods when it is not needed through the Quick Access Panel, and you should also turn off automatic network search if you are not roaming, so that the phone does not constantly try to scan the airwaves for a stronger signal from a foreign operator.