How to block numbers on the landline and the switchboard of a small business

Blocking numbers on a landline or a company switchboard does not work the way it does on a mobile. There is no app you tap with your finger. You have three layers: blocking on the handset itself, filtering at the switchboard or the operator, and registering with the Lista Robinson. This guide walks you through each one, in order, so your business phone stops ringing at the wrong moments.

On a mobile you block with a couple of taps. On a landline or a small-business switchboard things change: the control does not live in the device, it lives in the line, in the switch or in the contract with your operator. That is why many freelancers and small businesses give up and let salespeople and robots eat into their working day. There is no need. With a bit of order you can cut out most of the noise.

If you are coming from the mobile world, it helps to first review the guides on blocking on iPhone and blocking on Android by manufacturer. Here we focus on what is different: the home landline, the office landline and the VoIP switchboard.

Why is blocking on a landline different from a mobile?

A mobile is a computer with an operating system. It has native block lists, "silence unknown callers" filters and an app marketplace. A landline does not. A classic landline (analogue, or the one hanging off a fibre router) is usually a "dumb" terminal: it dials, it receives, and little else.

That means blocking can happen in different places depending on your setup:

• On the handset: some modern landline phones have a small directory of blocked numbers. Limited capacity (sometimes 30 or 50 numbers) and awkward to manage.
• On the operator's router: many fibre routers include a "call blocking" section in their web panel. There you can add specific numbers or enable the rejection of anonymous calls.
• At the operator: contracted filtering or "blacklist" services that are applied before the call even reaches your home or office.
• At the switchboard (if you have one): this is where a small business has the finest control, especially if you use VoIP.

The practical rule: the higher up you block (operator or switchboard), the fewer times the phone rings and the less it depends on any one device. Blocking on the handset is the last resort, not the first.

What options do I have depending on my type of line?

Before touching anything, work out what you have. A home landline is not the same as a virtual switchboard with twenty extensions. This table summarises the blocking routes by setup:

If you do not know which group you are in, here is a hint: if your office phone plugs into a network cable (RJ45) rather than the classic telephone socket, it is almost certainly VoIP and there is an administration panel behind it.

How do I block on a home landline phone?

For the home landline you have two fronts. Do them in this order.

1. Log into the router panel. It is usually at an address like 192.168.1.1 from your browser, using the username and password printed on the sticker on the device. Look for a section called "Phone", "VoIP" or "Calls".
2. Enable the rejection of anonymous calls. Many commercial spam calls hide their number. Rejecting calls without a caller ID cuts out part of the problem in one go, although it may also block someone legitimate who calls with their number hidden. You decide the balance.
3. Add specific numbers to the router's block list. Each number that bothers you, write it down and add it. Remember that caller ID spoofing means many spammers change their number constantly, so this list is never "finished".
4. Use the phone's own block list as a backup, especially if the router does not allow many entries.
5. Do not return odd missed calls. If someone hangs up on the first ring from an unknown number, do not call back: it could be a wangiri call or a premium-rate bait.

The weak point of this approach is that the spam number keeps changing. That is why, in parallel, it is worth registering with the Lista Robinson (we cover it below) and reporting the numbers so the community can identify them.

How do I set up blacklists on a VoIP switchboard?

This is where a small business really comes out ahead. A VoIP switchboard (Asterisk, 3CX, FreePBX, a virtual switchboard from your operator or a cloud PBX-type panel) lets you filter before any extension rings. The menu names change from system to system, but the concept is the same.

These are the techniques that work best in a business:

• Global blacklist. Almost all switchboards have a table of blocked numbers that applies to the whole company. It is the equivalent of the mobile block list, but centralised. A single change protects the entire workforce.
• Blocking by pattern or prefix. Instead of blocking number by number, you can create a rule that rejects whole ranges. For example, cutting off premium-rate prefixes that your business never needs to receive. To find out which ones, see the prefixes reference.
• Rejection of calls without a caller ID. Just like on the home router, but at company level: anonymous calls do not get through, or they go straight to voicemail.
• Time rules. Outside business hours, you divert everything to an answering machine. Spam that calls at odd hours stops bothering anyone.
• Filter IVR (voice menu). A spam robot rarely presses "1 to speak to a sales rep". A simple one-step IVR filters out a good chunk of automatic dialers without getting in the way of a human customer.

A note from the team: a switchboard does not tell "spam" from "customer". It only applies the rules you write. Start with broad blocks (anonymous, premium prefixes, hours) and then fine-tune with specific numbers. Document every rule so the next person who touches the switchboard knows why it is there.

If you have a physical switchboard (a PBX hanging on the wall) rather than VoIP, the logic is the same but it usually requires getting into the equipment's configuration or asking your maintenance provider. Ask explicitly for: a global blacklist, rejection of anonymous calls and time rules.

Is the Lista Robinson useful for businesses?

Yes, and it is the piece most people forget. The Lista Robinson is Spain's official advertising exclusion file. When you register, the companies signed up to the system must stop directing advertising at you through the channels you mark (phone, SMS, postal mail, email) unless you have a prior contractual relationship with them.

It is worth understanding clearly what it does and does not do, because it is not a technical block:

The conclusion is the same one we explain in the classic comparison of the Lista Robinson versus in-app blocking: you do not pick one or the other, you use both. Robinson reduces unwanted legitimate marketing; technical blocking kills aggressive spam and, above all, fraud, which Robinson does not touch.

A nuance for freelancers: if your business number is also your personal number, or is heavily exposed on websites and directories, the Lista Robinson helps but does not work miracles, because a lot of spam comes from those who have never respected that list. There your real defence is technical filtering plus community reporting.

And fraud? Blocking is not enough

Blocking numbers reduces the noise, but there is one type of call that a blacklist alone does not solve: fraud aimed at businesses. Small businesses are a tempting target because they handle money and often answer the phone out of commercial obligation.

Some patterns worth knowing in a business setting:

• Fake technical support that asks you to install a remote-access program "to fix a problem". According to the data and cases compiled by INCIBE, this fraud remains very active. No legitimate party asks you for remote access on a call you did not request.
• Fake electricity or gas sales reps who introduce themselves ambiguously to get hold of your CUPS or your IBAN. Always verify through your provider's official channel.
• Impersonation of suppliers or your bank by phone. If in doubt, review how to check whether a call from your bank is real.
• AI-cloned voice used to impersonate an executive and authorise an urgent transfer. The golden rule: hang up and verify through a channel you already know, never with the details given to you on the call.

For all of these, no blacklist saves you on its own, because the originating number is usually faked and keeps changing. What saves you is the internal protocol: verify through a known channel, do not give out data or access on incoming calls, and train the team that answers the phone. You have a good starting point on how to read the risk signals of a number.

Where do I report, and who do I turn to?

Blocking protects your business; reporting protects everyone else. When you receive a spam or fraud call on the landline or switchboard:

1. Identify the number. Write it down exactly as it appears, with the prefix. If it was an SMS campaign to a company mobile, save the message.
2. Check it on NoCall. Look up the number in the spam number directory to see whether others have reported it and what kind of nuisance it is.
3. Report it. Add your experience so the next person who gets that call has an easier time. It is the same community principle that feeds our trends and the ranking of operators with the most spam numbers.
4. If it is fraud, report it to the authorities. The reference channel in Spain is INCIBE, with its cybersecurity helpline 017 (also via the free phone number 900 116 117 and through its WhatsApp and web channels). For a business, it is also worth keeping an internal record and, if there was a financial loss, going to the Policía or the Guardia Civil.

If you want to understand the landscape better before configuring your filters, it will help to read the overview of phone spam in Spain and the Q2 2026 threat report, where we explain the patterns that most affect individuals and businesses.

Your plan in five steps

So you do not lose your way, this is the recommended order for a small business starting from scratch:

1. Register your number with the Lista Robinson. It is free and cuts out unwanted legal marketing in the medium term.
2. Set up blocking as high up as you can. If you have a VoIP switchboard, set up the global blacklist, the rejection of anonymous calls and the time rules. If you only have a landline, use the router panel.
3. Block prefixes your business never needs, such as premium-rate ones. Check the prefixes guide so you do not cut off something useful.
4. Train your team on phone fraud: never give out data, remote access or transfers in response to an unsolicited incoming call.
5. Report and check numbers on NoCall as a routine, not as a one-off reaction.

Phone spam in a company is not eliminated in one go, but it can be reduced until it becomes negligible when you combine the three layers: Lista Robinson, technical filtering and an internal culture against fraud.

Have you received a suspicious call on your business landline or switchboard? Check it and report it in the NoCall directory. Every report helps the next freelancer or small business recognise that call sooner and not lose another minute. And if you want to keep fine-tuning your defences, drop by our guides and the blog.