Calls from blacklisted numbers on Android often go through due to a conflict between the built-in blocking function, custom firmware of the smartphone and the specifics of call routing by the mobile operator, which creates the illusion of a system failure when trying to weed out spam or unwanted contacts.
To understand the nature of this phenomenon, it is necessary to consider the architecture of processing incoming calls. Call blocking can occur at different levels: directly on the device, on the SIM card side or in the cellular infrastructure. When you block a contact through the standard Phone app, the command is executed locally. However, if the call was already routed by the network before the filter was activated, you will hear a beep or see a notification.
In this article, we will analyze in detail the technical reasons why blocked numbers continue to call, and offer working methods to solve the problem. You will learn about hidden settings, the impact of technology VoLTE and how to create a truly impenetrable barrier to unwanted communication.
Differences between blocking on the device and on the operator's side
The first thing you need to understand is that your smartphone and your carrier are two different security systems. When you blacklist a number through the menu Call settings, you instruct the phone's processor to ignore a specific signal. But the signal itself has already reached your device. The operator sees this call even before it goes on air.
Local blocking Android works on the principle of a software filter. The phone receives the incoming data packet, checks the number against the database of prohibited contacts and, if a match is found, immediately resets the connection or mutes the sound. The problem is that in this short period of time the screen can light up and the vibration can work. This depends on the speed of the specific launcher and the version of the operating system.
Blocking on the operator’s side (“Antispam” or “Blacklist” from the provider) works more efficiently in terms of silence. The call simply does not reach your phone because it is rejected at the network switch. The subscriber hears short beeps or a message about unavailability, and your device does not receive a signal at all about the incoming connection.
⚠️ Attention: The blocking service on the operator’s side is often paid or requires a separate connection through your personal account. Free lists on your phone are not automatically synchronized with the provider’s network.
For complete silence, use a combined method: add the number to the black list on your phone AND activate the blocking service from your telecom operator.
The influence of VoLTE technology and network protocols
Modern 4G and 5G networks use technology VoLTE (Voice over LTE), which transmits voice as a data stream via the Internet protocol. This improves the quality of communication, but complicates the work of built-in blockers. In older 2G/3G networks, disconnection was initiated more easily, while in a 4G packet network, the call signal can pass through other gateways, bypassing the standard filters of the Phone application.
Some users note that after turning on or off VoLTE The behavior of the blacklist is changing. This is due to the way the smartphone modem handles SIP (Session Initiation Protocol) signaling. If the phone's firmware is not optimized to correctly handle rejecting calls in VoLTEmode, the phone can accept the call, show it on the screen, and only then reset it programmatically.
In addition, there are routing features when roaming or switching between towers of different standards. If during an incoming call the phone switches from 4G to 3G mode (or vice versa), a momentary glitch in the software filter may occur and the call will pass.
| Type of blocking | Where it happens | What the subscriber sees | Reliability |
|---|---|---|---|
| Local (Android) | On the smartphone | Beeps, then reset | Medium (the screen may light up) |
| Operator | On the server communication | "Subscriber is busy" or unavailable | High (the call does not reach) |
| Third-party applications | On a smartphone (application) | Depends on access rights | High (if you have root or special rights) |
Features of manufacturers’ shells: Samsung, Xiaomi, Pixel
Clean Android and custom shells from manufacturers implement the blocking function in different ways. This is one of the main reasons why the blacklist works perfectly on one phone, but not on another. For example, in smartphones Samsung with shell One UI the settings are located deep in the call menu, and sometimes users block a contact only in the call log, and not in the global list.
Devices Xiaomi (shell MIUI or HyperOS) often have powerful antispam built in, which may be disabled by default or configured too softly. Here it is important to check whether the “Blocking unknown numbers” mode is activated or whether the contact is added to the system black list, and not simply deleted from the phone book.
On smartphones Google Pixel a machine learning algorithm is used to identify spam. Sometimes the system marks a call as “Suspicious”, but does not block it completely, allowing the user to decide whether to answer or not. This may be perceived as a blocking failure, although in fact it is a filtering function.
⚠️ Attention: Settings interfaces change with each software update. If you do not find the “Black List” item in the usual place, use the search in the settings by entering the request “Blocking”.
Samsung Secret Setting
In some versions of One UI there is a hidden testing menu. Enter the code ##4636## in the dialer, go to “Phone Information” and check the forwarding settings. Sometimes resetting the forwarding settings solves the problem of calls getting through.
The problem of hidden numbers and international codes
One of the most common reasons for “breaking through” the blocking is a change in the number format. If you have blocked a number in the format +79001234567and the spammer calls from 89001234567 or via Internet telephony with a spoofed number, the phone perceives this as a new, unknown contact. Device-level identification systems are not always able to bring different record formats to a single standard before checking the blacklist.
There are also calls from hidden numbers (AON disabled). Standard blocking for a specific number is powerless here, since the incoming data packet does not contain numbers for comparison. To protect against such calls, you must use the “Block all hidden numbers” function, which is available in the settings of many modern smartphones.
Fraudsters often use number pools by changing the last digit or operator code. Blocking one specific number does not prevent calls from neighboring numbers in the same range. In this case, it is more effective to use mask blocking or third-party applications with a common database of spam numbers.
- 📞 Different formats: Block the number in the international format (+7...) to cover options with 8... and without a code.
- 👤 Hidden number: Activate the "Reject calls from hidden callers" option in call settings.
- 🌐 Internet calls: Calls through instant messengers (WhatsApp, Telegram) are not blocked by the system black list of the phone, they need to be blocked inside applications.
The system black list reacts only to the exact matching number digits. Changing the input format or replacing the number makes blocking ineffective.
Third-party applications for enhanced protection
If the built-in tools Android fail, specialized applications like Kaspersky Who Calls, NumBuster or Call Blockercome to the rescue. These apps have deeper access to the telephony system and often use cloud databases updated in real time.
The main advantage of such solutions is the ability to block not only by number, but also by characteristics (for example, “all numbers starting with 800” or “all private numbers”). However, they require broad permissions to function correctly, including access to call logs and contacts, which raises privacy concerns for some users.
It is important to configure the application correctly. Often the default mode is “Warn about spam” rather than “Block”. You need to go to the application settings and select hard blocking mode. It is also worth checking whether the application conflicts with system energy saving, which can “kill” its background process, making it impossible to intercept the call.
☑️ Setting up a third-party blocker
Radical measures: Do Not Disturb mode and forwarding
When nothing helps, you can use the Do Not Disturb (Do Not Disturb) mode. In this mode, the phone will ignore all incoming calls, except those included in the exception list (for example, “Favorites”). This is a guaranteed way to stop any calls, but it requires discipline: you may miss an important call from a doctor or courier if you forgot to add it to the white list.
Another method is to set up conditional forwarding. Through the engineering menu or operator settings, you can configure all incoming calls to be forwarded to a non-existent number or to voice mail if the call comes from a specific contact (this function depends on the operator’s capabilities). The command to check the forwarding status usually looks like *#61#.
*#61#
This command will show which number calls are forwarded to if you do not answer. Knowing this, you can manage the flow of calls more flexibly. However, remember that call forwarding may incur a charge depending on your tariff plan.
⚠️ Attention: Do Not Disturb mode may block repeat calls from the same number for 15 minutes. Make sure this option is disabled if you are expecting an important urgent call from a stranger.
Use Do Not Disturb mode with a schedule. Set up automatic switching on at night or during rest hours so as not to be distracted by possible blocking breakthroughs.
Why calls go through after a factory reset or update
Users often notice that after updating the firmware Android or resetting the phone to factory settings, the blacklist is cleared or stops working. This occurs because the database of blocked numbers is stored in the local contacts database file, which may be overwritten when the system Phone application is updated.
When updating software, developers can change the data storage structure or filtering algorithms. What worked in Android 11 may behave differently in Android 13 due to changes to Google's security policies that restrict apps' access to telephony. Therefore, after major updates, you should always double-check your blocking settings.
In addition, synchronizing contacts via Google Account sometimes restores old entries, but does not restore the blacklist settings, since they are often tied specifically to the device and not to the cloud. This means that when you change your phone, you will have to create a black list again, unless you use specialized applications with cloud backup of settings.
Is the black list restored when you change the SIM card?
No, the black list configured through the phone menu is tied to the device, not to the SIM card. If you move the SIM card to another phone, the lock will not work. Blocking from the operator, on the contrary, is tied to the phone number and will work on any SIM card with this number.
Can a virus disable the blacklist?
Theoretically, malware with administrator rights can change system settings, including disabling blocking. However, on modern versions of Android with Google Play Protect enabled, this is unlikely. More often, the reason is crooked settings or network features.
Does the phone block calls in airplane mode?
In airplane mode, the radio module is turned off completely, so calls physically cannot go through. However, as soon as you turn off Airplane mode, the accumulated calls (if the operator queued them) may arrive. The black list will already be active at this moment.
What to do if the number is blocked, but SMS messages are received?
The black list in the “Phone” application only blocks voice calls. To block SMS, you need to add the number to the blacklist of the Messages application or use third-party spam blockers that filter both calls and messages.
Why does a blocked number ring with a dial tone?
The caller hears the dial tone, not you. If you see the call screen, it means the signal has reached the phone. If you hear a dial tone in the handset after picking up, this may be a recording or a network failure. Usually, when blocked, the call is dropped instantly, and the caller hears short busy beeps.