Using a smartphone as a primary tool for business or personal communication often requires having multiple phone numbers. Fortunately, modern mobile devices based on the operating system Android provide a built-in “Second Line” (or “Call Switching”) function, which allows you to handle two calls simultaneously without the need to physically have two SIM cards in the slots. This technology, known as Call Waiting, makes it possible to put the current call on hold and answer an incoming call from another subscriber, and then easily switch between them or join into a conference.
Many users are faced with a situation where the incoming signal is simply dropped or sounds busy, although this option should be active by default in the phone settings. However, depending on the device model, firmware version and operator's tariff plan, the settings may be hidden or disabled. The correct configuration of this function turns your smartphone into a powerful communication center, allowing you not to miss important business calls even during an informal conversation.
In this guide, we will analyze in detail the algorithm for activating the second line, the features of working with two physical SIM cards and app numbers. You will learn how to avoid common setup mistakes and what to do if the call control menu is not included in the standard interface. Understanding the principles of operation network services will help you effectively manage your telephone traffic.
Activating the call switching function in the settings
The first step to organizing work with two lines is to check the system parameters of your device. The standard path to the necessary settings may differ slightly depending on the manufacturer's shell, for example MIUI, OneUI or ColorOS, but the general menu logic remains the same for the entire ecosystem Android. You need to open the Phone application, which is used to make calls, and find the menu of additional options, usually indicated by three dots in the corner of the screen.
After going to the call settings, you should look for the section responsible for additional operator services. In some versions of the system, this item may be called “Operator Settings” or “Advanced Settings”. This is where the switch responsible for notification of the second call is hidden. If the slider is inactive, the system will automatically reject repeated calls, considering the line busy.
⚠️ Attention: Changing the parameters in this menu sends a USSD request to the server of your mobile operator. Make sure that you have a stable network signal, otherwise the setting may not be applied correctly.
In some cases, especially on older smartphone models, the option may be hidden deep in the “Special” system menu. capabilities" or require manual code entry. To force activation of the service, you can use a universal command that works for most telecom operators. Enter the following code when dialing:
*43#Pressing the call button after entering this combination should initiate a request to the network. If the service is connected successfully, you will receive a corresponding notification on the screen. If you receive an error message or the service is not supported, this may indicate limitations in your tariff plan or technical work on the side of the communication provider.
☑️ Checking the second line settings
Features of working with two physical SIM cards
Modern smartphones are often equipped with two physical slots for SIM cards, which creates confusion in the concept of “second line”. Here it is important to distinguish between the function Call Waiting (holding a call on one number) and the possibility of simultaneous activity of two different numbers. When two SIM cards are installed in the device, for example Sim 1 and Sim 2, each of them can independently support the second call waiting mode.
When there is an active call on the first SIM card, an incoming call to the second SIM card may be processed differently depending on the phone settings. In most cases, if you do not use the function 4G/5G calls (VoLTE), the second line may temporarily become unavailable during a conversation on the first due to the radio module switching to 2G/3G mode. This is a technical limitation of the radio chip architecture, and not a software bug.
To ensure full operation of both lines at the same time, it is recommended to activate support for voice calls over the LTE network. This allows the radio module to support voice channel and data transmission simultaneously, without interrupting the registration of the second SIM card in the network. You can check the presence of this function in the SIM card management menu, where for each slot there should be a separate switch Allow calls via LTE.
| Option | One SIM (Second line) | Two SIM (Without VoLTE) | Two SIM (With VoLTE) |
|---|---|---|---|
| Receive a call during a call | Possible (to the same number) | Second SIM is not available | Both SIMs are active |
| Technology | Call Waiting | Frequency switching | Packet voice transmission |
| Internet dependence | No | No | Requires 4G coverage |
| Battery consumption | Standard | Increased when searching for a network | Optimal |
If your operator does not support VoLTE in the region stay, then when talking on the first SIM card, the second one will temporarily “fall out” of the network. Subscribers trying to call the second number at this moment will hear a busy signal or get an answering machine. This is normal behavior for devices that do not support new generation technology. DSDS (Dual SIM Dual Standby) new generation.
Using Internet instant messengers as a second line
An alternative and increasingly popular way to organize a second telephone line is to use applications for calls over the Internet, such as WhatsApp, Telegram or Viber. In this context, a “second line” is a virtual number or account linked to another phone or dedicated service. This solution allows you to receive calls in parallel with regular cellular communications, since a separate data transmission channel is used.
To set up this scheme, you will need to install an additional application that emulates the operation of a telephone. There are specialized services that provide rental of virtual numbers for receiving SMS and calls. After registering in such an application, you get the opportunity to make and receive calls using an Internet connection Wi-Fi or mobile traffic.
The main advantage of this approach is complete independence from the settings of the cellular operator regarding call waiting. You can talk on a regular SIM card and receive a call in the messenger at the same time, simply by switching between active windows or using the pop-up notification function. However, the quality of communication here directly depends on the speed and stability of your Internet connection.
⚠️ Attention: When using Internet calls while roaming, significant traffic charges may apply. Always check data rates before traveling abroad.
Some advanced users set up forwarding from the main SIM card to a virtual number in emergency cases. This requires complex configuration in the operator’s personal account, but allows you to create a flexible system for processing incoming calls. remember that forwarding paid numbers may lead to unexpected costs.
To save battery power when using instant messengers as a second line, disable auto-downloading of media files in the application settings.
Managing conference calls and merging calls
The second line function opens up opportunities not only for alternate communication, but also for organizing group conversations. When you hold the first call and answer the second, a control panel with buttons Merge or +appears on the smartphone screen. Pressing this key creates a conference call in which all three participants (you and the two interlocutors) hear each other at the same time.
The process of creating a conference is intuitive, but has its own technical nuances. After calls are merged, the system considers that two phone lines are busy, so the ability to accept a third incoming call is usually blocked. In this state, you can manage participants: mute the microphone for a specific interlocutor or exclude him from the conversation without interrupting the conversation with others.
It is important to note that the maximum number of conference participants is limited by the capabilities of your telecom operator and tariff plan. The standard limit is often 5-6 people, but business plans may offer expanded options. When combining calls, tariffs are charged separately for each connected line, that is, you pay for two minutes of conversation for each minute of the conference.
If the merge button is inactive or disappears, this may indicate that one of the participants in the conversation is using a device or network that does not support this feature. In such cases, the only option left is to switch between subscribers in standby mode.
The secret of a quick conference
On some smartphones, you can start a conference by simply dialing the number of the second subscriber during the first conversation through contacts, without using the "Add call" button manually.
Possible problems and ways to resolve them
Despite its apparent simplicity, users often encounter a situation where the second line does not work properly. The most common problem is the absence of the “Call Switching” menu item in the phone settings. This often occurs on devices in which the manufacturer has simplified the interface or hidden technical settings from the user. In this case, the only solution is to use USSD codes or contact the operator's support service.
Another common cause of failures is a conflict in network modes. If the phone is configured to work exclusively on networks 5G, and the coverage in your area is unstable, the call waiting function may work intermittently. Switching the network mode to 4G/3G/2G (Auto) often solves the problem of stability of registration on the network and correct operation of holdover services.
It is also worth considering the influence of third-party applications for calls. If you have installed an alternative dialer from the store Google Play, it may intercept call control and ignore the second line system settings. Try temporarily setting the standard Phone application as your default app and test the function.
⚠️ Warning: Resetting your network settings to factory defaults will delete all saved Wi-Fi passwords and Bluetooth pairs. Use this option only if other methods have failed.
In rare cases, the problem may lie in the SIM card itself. Older cards that have been in use for more than 5-7 years may not process modern network commands correctly. Replacing the SIM card with a new one in the operator's salon often eliminates strange errors in telephony operation.
If the second line function is not activated by the code *43#, the problem is almost certainly on the operator's side or in incompatibility of the tariff, and not in the phone.
Frequently asked questions (FAQ)
Can I connect a second line if I only have one SIM card?
Yes, the “Second Line” (Call Waiting) function works on one phone number. It allows you to receive a second call to the same number, putting the first conversation on hold.
Is the call switching service paid?
In most tariff plans of Russian and foreign operators, this service is enabled by default and is free. However, for minutes of conversation during a hold or conference, charging is according to your main plan.
Why can’t I hear a dial tone when they call me during a call?
This may mean that the service is disabled in the phone settings or on the operator’s side. Also check to see if Do Not Disturb is turned on, which may block audio notifications for a second call.
Does second line work when roaming?
Technically, the feature is supported, but its operation depends on the agreement between your home operator and the partner network in the host country. It is recommended to clarify the roaming conditions before traveling.
How to disable the second line if it is bothering me?
To disable the service, use the USSD code #43# and press the call button. You can also uncheck the box in the settings of the “Phone” application in the “Call Switching” section.