Blocking basics: numbers, and what blocking actually does
Blocking a number on Android is two taps from wherever you see it: in the Phone app, Recents, tap the number, Block or Report spam; in Messages, long-press the conversation, Block, and check 'Report spam' while you are there. To block a number you have not been contacted by, Phone app, three-dot menu, Settings, Blocked numbers, Add a number. The blocked list in that same screen is also where you unblock, no drama, entries toggle freely.
What blocking does: calls from the number go straight to voicemail without ringing (and on many carriers, without even reaching voicemail), texts arrive nowhere you see, and crucially, the blocked party receives NO notification of being blocked, their call simply rings once and diverts, indistinguishable from your phone being off. What it does not do: block the person, only the number, a determined caller with a new SIM starts fresh, which is why the harassment section below goes beyond simple blocking. Blocking also does not affect other channels: a number blocked in Phone can still reach you on WhatsApp until blocked there separately, each app maintains its own list.
Two useful precision tools complete the basics. Blocking calls without blocking texts (or vice versa) is not natively granular, but the practical equivalents exist: silence a contact's calls via Do Not Disturb exceptions while leaving messages alive, or mute a conversation's notifications in Messages while technically receiving them. And for the reverse need, ensuring someone ALWAYS gets through, star them as a favorite and set Do Not Disturb to allow starred contacts, the configuration that lets you silence the world at night without silencing family.
The spam-call defense: caller ID, filtering and the unknown-caller wall
Blocking individual spam numbers is bailing the ocean, spammers rotate numbers endlessly, so the real defense is filtering by behavior, and Android ships it built-in. In the Phone app: Settings, Caller ID and spam, and enable both 'See caller and spam ID' and 'Filter spam calls'. The first labels incoming calls (Suspected spam, Telemarketing) using Google's intelligence; the second silently diverts the confident-spam tier so your phone never rings at all. These two toggles, off by default on many phones, are the single biggest quality-of-life upgrade in this guide.
The next wall up is silencing unknown callers entirely: numbers not in your contacts ring silently or divert to voicemail (Phone app settings on many brands, or via Do Not Disturb configured to allow contacts only). It is drastic and gloriously effective for heavy-spam sufferers, with the known cost: deliveries, doctors' offices and callbacks from real businesses land in voicemail, so pair it with the habit of actually checking voicemail, and pre-save numbers when expecting a call. Google's Call Screen feature, where available, is the elegant middle: the assistant answers unknown calls, asks who is calling, and transcribes live, letting you pick up for the plumber and ignore the robot.
Carrier-level tools stack underneath: the major carriers run free spam-blocking services and apps (activation is often a settings toggle or a short code, and our secret codes tool documents the useful dialer codes generally), and numbers can be reported to the carrier by forwarding, which improves the shared filters. Resist the third-party 'spam blocker' apps that demand full call, contact and SMS access as their price: the built-in Google plus carrier stack now equals or beats them without handing your entire communication graph to an ad-funded company, the same no-cleaner-apps logic as our popup-ads guide.
Spam texts and smishing: filtering, reporting, and never clicking
For SMS, Google Messages carries a real spam filter that most people have never enabled: Messages, profile picture, Messages settings, Spam protection, on. Suspected spam then diverts to the Spam and blocked folder silently, and the per-conversation Block and report spam action both silences the sender and trains the filter, report generously, it works. Check the spam folder occasionally for false positives (appointment reminders and delivery notices occasionally land there), and know that alphanumeric senders ('PROMO-XY') block exactly like numbers.
Smishing, scam texts impersonating deliveries, banks and prize draws, deserves its own reflexes because the goal is your click, not your reply. The rules: never tap links in unexpected texts, period, if a delivery or bank text might be real, go to the app or official site directly rather than through the message's link; never reply at all to obvious spam, even 'STOP', except to senders you know are legitimate businesses (replying to criminals confirms your number is live and harvests it for more); and forward smishing attempts to your carrier's reporting number where offered, which feeds the network-level filters.
Special text categories have special handling. Verification-code texts you did not request mean someone is trying to log into an account of yours: do not share the code with anyone (no legitimate party ever asks for it), and change that account's password today. Group-spam adding you to MMS groups is silenced by leaving and blocking the sender, and Messages' settings can disable group texts from unknown senders. And subscription-scam texts billing through your carrier ('you subscribed to horoscopes') are fought at the carrier: demand the charge's removal and ask for a purchase block or premium-SMS block on the line, a free carrier-side switch that closes the entire scam category.
Harassment, stalking and the cases beyond blocking
When the unwanted contact is a person rather than a robot, escalate deliberately. Document BEFORE blocking: screenshot the messages and call log with numbers and timestamps visible (our screenshot guide's scrolling captures take whole threads), export conversations where the app allows, and email the evidence to yourself for timestamped custody, because blocking hides future contact but a report needs the history. Then block across every channel the person can reach: Phone, Messages, WhatsApp, social apps, email, each separately, and consider whether shared accounts or family plans give them other visibility.
The number-rotation problem, a harasser calling from new numbers, is met with the unknown-caller wall from earlier (contacts-only ringing plus Call Screen), which converts their new-SIM game into silent voicemails you review on your terms. For serious cases, the formal tools exist and work: carriers maintain harassment procedures and can change your number free or cheaply in documented cases; police reports create the paper trail that protective orders and prosecutions require, and your saved evidence is exactly what they will ask for. Safety planning resources go beyond this guide's scope, but the technical posture, document, block everywhere, wall unknown callers, involve the carrier and police early, is the consistent foundation.
Close with the maintenance habits that keep the quiet: review the blocked list and spam folder monthly (two minutes), keep the filtering toggles on after system updates (they occasionally reset), report spam rather than just deleting (each report improves the shared filters), and teach the two-toggle setup (caller ID plus spam filtering, SMS spam protection) to the family members whose phones ring all day, the same ninety-second favor as the notification-spam cleanup in our ads guide. A properly configured Android is startlingly quiet, and everything in this guide is free, built-in, and reversible.