# The best API against spam calls in 2026: an honest comparison

> Number lookup, caller reputation, STIR/SHAKEN or deepfake detection? How spam call APIs differ, which one fits your use case and what to check before you buy.

Source: https://identityphone.com/en/blog/best-spam-call-blocking-api/
Language: en · Published: 2026-10-05 · Updated: 2026-10-05 · Publisher: Identity Phone

**Short answer:** there is no single "best" spam call API – there are four different kinds of API that solve four different problems. If you only need to know *whether a number is risky*, buy number intelligence. If you need to know *who is really on the line* – the problem that AI voice clones have made urgent – you need caller verification plus deepfake detection.

> Disclosure: Identity Phone is our product and is currently in development (early-access waitlist). We mention it where it fits and say clearly where other – already available – tools are the better choice.

## The four types of spam call API

| Type | What it answers | Typical providers | Best for |
|---|---|---|---|
| Number intelligence / lookup | "Is this number valid, mobile or VoIP, recently ported?" | Twilio Lookup, Telesign, Vonage Number Insight | Sign-up checks, SMS/OTP fraud, data hygiene |
| Caller reputation | "Have many people reported this number as spam?" | Hiya, Truecaller for Business, carrier analytics (e.g. TNS) | Warning labels, blocking robocalls in dialer apps |
| Network attestation | "Did the originating carrier vouch for this number?" | STIR/SHAKEN via your carrier (mainly US/Canada) | Reducing spoofed numbers on carrier networks |
| Identity & voice verification | "Is this really the person or company they claim to be – and is the voice human?" | Pindrop (contact centers), Reality Defender (deepfake detection), Identity Phone (in development) | Stopping impersonation, CEO fraud, "grandchild" scams, voice-clone attacks |

Most teams need a combination. The mistake we see most often: buying a reputation database and assuming it protects against targeted fraud. It does not – a scammer impersonating your CFO calls once, from a fresh or spoofed number with no spam history.

## 1. Number intelligence APIs

These APIs look up metadata about a phone number: whether it exists, the line type (mobile, landline, VoIP), the carrier and sometimes a risk score.

**Good at:** catching fake or disposable numbers during registration, reducing SMS pumping, routing.
**Not built for:** telling you whether an *incoming call* is a scam, and nothing about the voice on the line.

## 2. Caller reputation databases

Reputation providers aggregate signals from carriers, apps and user reports to label numbers as "spam likely", "telemarketer" or "fraud".

**Good at:** high-volume robocalls and known scam campaigns.
**Weak spots:** brand-new numbers, spoofed numbers that belong to someone innocent, and targeted attacks that call only once.

## 3. STIR/SHAKEN and network attestation

STIR/SHAKEN is a protocol for signing caller ID between carriers. In the US, the FCC required major voice providers to implement it on their IP networks from June 2021. A call gets an attestation level (A, B or C) that tells the receiving carrier how confident the originating carrier is about the number.

**Good at:** making large-scale number spoofing harder inside participating networks.
**Limits:** it is mostly a North American system, it breaks across legacy (TDM) and international links, and an "A" attestation only means the number was not spoofed – a scammer with a legitimately rented number still gets an "A".

## 4. Caller verification and deepfake detection

This is the newest category, driven by AI voice cloning. Research systems such as Microsoft's VALL-E (2023) showed that a few seconds of audio can be enough to imitate a voice, and cloning tools are now widely available. In 2024 the US FCC ruled that AI-generated voices in robocalls count as "artificial" voices under existing telemarketing law – a sign of how fast the problem grew.

Two building blocks matter here:

- **Identity verification** – proving cryptographically that the caller is a known person or organisation, independent of the displayed number.
- **Synthetic voice detection** – analysing the audio for artefacts typical of generated speech and raising a warning during the call.

Contact-center vendors such as Pindrop and detection specialists such as Reality Defender focus on enterprise audio analysis. Identity Phone, which is currently in development, is being built to combine verified caller identity, number risk scoring and synthetic voice detection in one API – and in an app for people and teams who are not running a call center.

## How to choose: a checklist

1. **What is the threat?** Mass robocalls → reputation. Fake sign-ups → number intelligence. Impersonation of trusted people → verification + deepfake detection.
2. **Real-time or batch?** Incoming-call protection needs answers in well under a second.
3. **Coverage.** Ask for coverage in *your* countries – reputation data is usually strongest in the US.
4. **False positives.** Blocking a real customer or a family member is expensive. Ask how verdicts are explained.
5. **Privacy.** Call audio is sensitive personal data. Clarify where it is processed, whether it is stored and for how long – especially under GDPR.
6. **Pricing model.** Per-lookup pricing gets expensive at call-center scale; predictable subscriptions are easier to budget.

## Our recommendation

- **Developers validating numbers:** start with a number intelligence API.
- **Dialer and telecom apps:** add a caller reputation feed.
- **Banks, fintechs, contact centers and finance teams:** add caller verification and deepfake detection – this is where losses per incident are highest.
- **Individuals and families:** you do not need an API at all; use an app that verifies contacts and warns about cloned voices.

If you are in the last two groups, [join the Identity Phone early-access waitlist](/en/waitlist/) or [read about the planned API](/en/api/).

## FAQ

### What is the best API against spam calls?

It depends on the job. For validating numbers at sign-up, a number intelligence API (e.g. Twilio Lookup, Telesign, Vonage) is enough. To warn people about incoming spam, you need a caller reputation database (e.g. Hiya). To stop impersonation of trusted people – including AI voice clones – you need caller verification and synthetic voice detection, which is what Identity Phone (currently in early access) is being built for.

### Does STIR/SHAKEN stop spam calls?

No. STIR/SHAKEN lets a carrier sign that the calling number was not spoofed on its network. It does not say whether the caller is honest, and it does not detect cloned voices.

### Can an API detect AI-generated voices on a phone call?

Yes, specialised models analyse call audio for artefacts of synthetic speech. Detection is probabilistic, so it should be combined with identity verification rather than used alone.