B2B phone number finder: where numbers come from and what the rules say

B2B phone numbers come from public sources such as company websites and registers, from data that people or companies submit, from contributor networks and from a provider's own verification. Quality varies by region and seniority, so test a sample before you pay. Using a number is a legal question as well as a data one. This post explains both, and what to do with a number once you have it.

Nothing here is legal advice. Rules differ by country and by who the person is, and you should check your case with a lawyer.

Where do the numbers come from?

A phone number finder is a lookup over a database that someone built. The common sources are:

• Public pages and registers. A switchboard number on a company site, a number in a business register, a number on a conference speaker page. These are the most reliable for companies and the least useful for individuals, because they reach a reception desk.
• Submissions. People and companies who typed their number into a form that fed a data provider.
• Contributor networks. Users of a tool agree to share their address book or business cards, and the provider matches them.
• Verification. The provider tests a number, or checks it against another source, and marks it verified.

A provider should tell you which of these it uses, and how often records are checked. If it will not, treat the data as unverified.

How good are the numbers?

It depends on who you are looking for. A direct mobile number of a senior person at a small company in one market may be easy to find. The same person at a large company in another market may not be. Quality changes with country, company size, seniority and age of the record.

Test before you buy a large amount, and test on your own list.

1. Take 100 contacts you actually want, spread across the countries and roles you plan to work.
2. Run them through the finder.
3. Count how many returned a number, and how many of those were right, by checking a sample with a short, polite check.
4. Write the result as a rate with the base: "62 of 100 returned a number; 19 of 25 checked were right".

Do not trust a coverage percentage on a sales page. It describes the provider's database, not your list. Sellinger's contact database holds 700M+ contacts and includes verified emails and phone numbers, and the same rule applies to it: test a sample of your own, because coverage differs by region and role.

What does a lookup cost?

Prices differ by provider and by type of data. Phone numbers are often priced above emails because they are harder to get. In Sellinger, enrichment is a usage module that starts with a $10 credit, and the enrichment credits explained page says what each lookup costs. Check the current price of the lookup type you need on the pricing page before you plan a budget, instead of assuming it matches the email price.

Some providers try several sources in order and charge only for a hit, which lowers the cost of misses. The lead enrichment post explains how combining sources works.

What do the rules say?

In the EU, the GDPR applies to personal data, and a business phone number linked to a named person is personal data. You need a lawful basis for using it. For B2B outreach, many teams rely on legitimate interests, which requires a balancing test you can document; see the glossary entry. Where you did not collect the data from the person, Article 14 requires you to tell them who you are, why you hold their data and where you got it, usually within a month or at the first contact. The official text is on EUR-Lex. People also have the right to object, and an objection to marketing must be respected.

In the UK, there is a separate rule for calls. The ICO says that before you make live B2B calls, you need to screen against both the CTPS and TPS registers, because some businesses register with one and some with the other. It also says the PECR rule on email does not apply to corporate subscribers, so B2B email and text can be sent to a corporate body, as long as you do not disguise your identity and you give a valid address for opt out. Sole traders and some partnerships are individual subscribers and need consent or a soft opt in (ICO guidance, read 25 October 2026). If you cannot tell whether a contact is a corporate or an individual subscriber, the ICO's guidance is to treat it as an individual subscriber.

Elsewhere, the rules differ. Some countries keep do not call registers, and some regulate messaging apps. Look up the rule for the country of the person you want to reach, not the country you work from.

None of this tells you that a number is safe to use. It tells you to ask, before you use one, what the lawful basis is, how you will tell the person, and how they can stop you.

What can you do with a number besides calling it?

Many teams find that the number is more useful as an identifier than as a way to ring someone.

• Match records. A number helps to confirm that two entries are one person, so you do not write to the same lead twice.
• Reach someone on WhatsApp after they have replied elsewhere. If a lead answered on LinkedIn or email and prefers a message app, you can continue there. WhatsApp itself limits outbound messaging, so use it for people who already know you. Sellinger sends through your connected WhatsApp account and answers people who write first.
• Check that a contact is real. A number that matches a company's known switchboard region is a small sign the record is current.

Sellinger's channels are LinkedIn, email, WhatsApp, Instagram and live chat. A number found by enrichment becomes a lead field, and the agent works the lead in the channels you have connected.

How should you store and handle numbers?

• Keep a note of where each number came from and the date, so you can answer "how did you get my number?".
• Honor opt outs on every channel. In Sellinger, a contact who replies with an opt out such as STOP or unsubscribe goes on the team's suppression list, and the agent stops.
• Delete or anonymize on request. Sellinger has an erasure function that takes an email address, phone number or LinkedIn address, anonymizes the matching leads and adds the identifiers to the suppression list.
• Do not buy lists of unknown origin. If a seller cannot tell you the source, you cannot tell the person.

A short checklist before you use a finder

• Test 100 of your own contacts and record found and right rates with the base.
• Ask the provider for its sources and update frequency.
• Check the price of the exact lookup type.
• Write down the lawful basis and the notice you will send.
• Decide the use: matching, messaging after a reply, or something else.
• Set up opt out and erasure before the first message.

A phone number finder is a data tool with legal strings attached. Used with a tested sample, a clear basis and a way to stop, it is useful. Used as a shortcut around those three, it is a risk to your reputation and to the people on the list.