How to block unknown callers on Android without missing real contacts

Block spam and unknown callers on your Android dual-SIM phone while keeping your contact allowlist intact. Step-by-step setup with Hush.

Mar 30, 2022Updated Apr 22, 2026

Quick answer

You can block unknown callers on Android without missing real contacts by building a contact allowlist and routing everything else to voicemail. The key is configuring this per SIM, so your work line and personal line can have different rules (alongside any time or Wi‑Fi conditions you use for quiet periods). With Hush, you set these options independently for each SIM, which means blocking unknown callers on your work line does not affect your personal line at all.

What you need before you start

A dual-SIM Android phone with Hush installed
Your contacts saved in your phone's address book (the allowlist is built from saved contacts)
A voicemail account active on both SIMs
About 15 min for the initial setup

Step 1: Make sure your important contacts are saved

An allowlist only works if the people you want to reach you are saved in your contacts. Before touching any call-blocking settings, spend a few minutes reviewing your contacts app.

Add anyone who is likely to call you that you do not currently have saved. This includes:

Work colleagues who call occasionally but are not in your phonebook
Service providers (your doctor's office, your children's school, etc.)
People who might call from multiple numbers (save all their known numbers)

You do not need to be exhaustive. You are building a first version that you will refine. Add the obvious ones now.

Step 2: Configure unknown caller handling per SIM

Open Hush and go to the call filtering settings for your work SIM. Enable the unknown caller option. This tells Hush to intercept any call from a number not in your contacts.

Choose what happens to intercepted calls. The best option for most people is to decline the call silently so the caller can leave a voicemail. Exact behaviour depends on your Android version and carrier — on most devices this means:

You are not interrupted by spam or cold calls
Legitimate callers who are not in your contacts can still leave a message
You can call back anyone who leaves a voicemail with a real reason to talk

Note: Hush works with what Android exposes to apps. On some devices or carriers the call may ring briefly before being declined. Test on your device to confirm the behaviour.

Do the same for your personal SIM if you want unknown callers blocked there too. If you prefer your personal line to be more open (useful if you frequently receive calls from new numbers), leave the personal SIM filter off or set it to ring through with a low-priority notification.

Step 3: Set up a voicemail fallback

If you are going to block unknown callers, voicemail is your fallback channel. Make sure it is actually set up and working.

Call your own work number from another phone and let it ring until it goes to voicemail. Listen to the greeting. If it is the default carrier greeting with no name, record a custom message so that legitimate callers know they have reached the right person and are more likely to leave a message.

Keep the voicemail greeting brief: your name, that you will call back, and optionally an email address for non-urgent contact. You do not need a long explanation.

Step 4: Build your work SIM allowlist

Beyond saved contacts, you may have specific numbers that are not in your address book but should ring through. These could be:

Your office landline
A client's main switchboard number
A partner company's general number

In Hush, add these directly to the allowlist for your work SIM as raw numbers. They do not need to be saved as contacts, just added to the bypass list.

Keep the list intentional. The temptation is to add numbers broadly. Resist it. Every number you add is an exception to the rule you are trying to enforce.

Step 5: Handle the new-numbers-from-known-people edge case

The hardest edge case in any allowlist system is when someone you know calls from a number you have not seen before. Maybe a colleague gets a new mobile, maybe a client calls from their home phone.

You have two options:

Option A: Enable repeat caller exceptions. In Hush, enable the setting that allows through any number that calls twice in quick succession (within 3 min). The logic is that spam callers do not call back immediately. If someone calls twice, there is a higher chance it is legitimate. This is not foolproof, but it catches most genuine re-calls.

Option B: Check voicemail regularly. If someone important calls from an unknown number and leaves a voicemail, you call back and add their new number to your contacts. This keeps your allowlist tight but requires you to stay on top of voicemail.

Most people benefit from combining both: repeat caller exceptions on plus regular voicemail checks.

Step 6: Test the configuration

Before relying on this setup, test it with a safe scenario.

Ask a friend to call your work number from a number you have not saved. Confirm that:

The call does not ring on your phone
They can leave a voicemail
You receive the voicemail notification

Then ask a saved contact to call. Confirm their call rings through normally.

Two tests, 2 min, and you will know the configuration is working.

Common problems

I blocked a legitimate call from a real person. Go to your recent calls and find the blocked call. Add that number to your contacts or directly to your Hush allowlist. Then check whether there are other numbers from the same person you should add. For future-proofing, enable repeat caller exceptions so that genuine re-callers have a path through.

My work line is too strict and I am missing time-sensitive calls. This usually means the allowlist is too narrow. Review your voicemail log for the past week and see who called from unknown numbers. Add the numbers that belong to real contacts. You may also want to widen the repeat caller window or enable a notification (without a ring) for blocked calls so you can review them quickly.

Voicemail is not set up on one of my SIMs. Contact your carrier. Voicemail setup varies by carrier, but it is usually activated by dialling a short code or through the carrier's app. Without voicemail, blocked callers have nowhere to leave a message, which means legitimate callers who are not in your contacts will have no way to reach you.

FAQ

Does blocking unknown callers affect SMS messages too? In Hush, call blocking and SMS filtering are separate settings. Blocking unknown callers only affects incoming calls by default. If you also want to filter unknown SMS messages, enable that setting separately for each SIM.

What if I need to be reachable by new clients whose numbers I do not have? One approach is to keep your personal SIM open to all callers and use your work SIM as the line you share with existing contacts only. New clients or prospects can email you or reach you through a contact form before you exchange phone numbers. This keeps the relationship friction low without opening your work SIM to cold calls.

Can I see a log of blocked calls? Yes. Hush maintains a log of all blocked calls with the number, time, and SIM. You can review this log at any time and add any number to your allowlist directly from the log.