Twilio vs Vonage vs Telnyx: the carrier under a Dutch voice agent

The client sells solar maintenance contracts in Noord-Brabant. Their inside sales team was burning four hours a day on first-touch calls that ended in voicemail. We built them an outbound voice agent that does the dial, the Dutch greeting, the qualification, and the calendar handoff. It runs about 4,800 calls a week: roughly 60% mobile (06-prefix), 40% landline, 92% answered between 09:30 and 17:00 Amsterdam time.

The agent itself is boring. A small state machine, a Dutch TTS voice, a transcription loop, a webhook to HubSpot. The interesting part, and the part nobody writes about honestly, is the carrier underneath. We ran the same agent on Twilio, then Vonage, then Telnyx, six weeks each, same script, same hours, same target list segmented three ways. Here is what the invoices actually said.

What the per-minute rates look like once you strip the marketing pages

Published rates lie by omission. They quote you the headline number for a US-to-US call and let you assume Europe is similar. Europe is not similar, and the Netherlands has its own quirks because of how KPN and the mobile network operators bill termination.

Here is what we paid, per minute, for outbound calls originating from a Dutch number to a Dutch destination, across the six-week windows in Q1 and Q2 2026. These are blended rates including the small per-call setup fee divided by average call length (our average was 47 seconds, which matters more than you think).

Destination          Twilio       Vonage       Telnyx
NL landline (geo)    €0.0140      €0.0095      €0.0070
NL mobile (06)       €0.0480      €0.0410      €0.0285
NL 088 (non-geo)     €0.0190      €0.0140      €0.0095
Per-call setup       €0.0050      €0.0040      €0.0000
Number rental/mo     €1.15        €0.90        €0.50

At 4,800 calls a week averaging 47 seconds, with the 60/40 mobile/landline split, the weekly carrier bill landed at roughly €178 on Twilio, €151 on Vonage, and €105 on Telnyx. Over a year that is €9,200 vs €7,850 vs €5,460. Same agent, same call quality on the listener's end, same answer rates within statistical noise.

The Dutch-number-portability tax

This is the part nobody publishes. If you start on Twilio and want to move your Dutch number to Telnyx six months later, you discover that ACM (the Dutch regulator) treats number portability as a right, but the carriers treat the operational side of it as a cost centre.

Twilio will release a Dutch geographic number within 5 to 10 business days if you submit a clean LOA (Letter of Authorisation) and the receiving carrier files the port. We have done this four times. The median was 8 business days. Twice it stalled because the address on the number registration did not exactly match the KvK (Chamber of Commerce) address on the company that owned the number. Once because the receiving carrier filed the port code wrong.

Vonage was slower. Two ports took 11 and 14 business days respectively. Their support escalation path goes through a US queue, which means the loop between "KPN rejected this for reason X" and "here is the fixed LOA" runs in 24-hour increments because of the timezone gap.

Telnyx was the fastest in our sample. Both ports completed in 4 and 6 business days. They have a Dutch-speaking porting team and they pre-validate the LOA against the KvK registry before submitting. They also do not charge a porting fee for inbound ports of Dutch numbers, which Twilio does (€7.50 per number) and Vonage does inconsistently (sometimes €15, sometimes waived, no documented rule).

Where the cheaper carrier costs you somewhere else

Telnyx wins on price and porting. It does not win on everything. The trade-offs are real and you should know them before you commit.

The Twilio Programmable Voice SDK and the Media Streams API are more mature. If you are doing real-time bidirectional audio with a model that needs sub-200ms round-trips, Twilio's edge locations and their Media Streams documentation are honestly better. We measured median round-trip audio latency from a Dutch mobile to our agent backend (in eu-west-1) at 142ms on Twilio, 168ms on Vonage, and 189ms on Telnyx. Telnyx has been improving this; six months ago it was over 220ms.

Vonage's strength is the rest of their stack. If you are also doing SMS, WhatsApp Business, and email verification through the same vendor, the consolidated billing and the unified dashboard are worth something. Their voice product alone is not the cheapest or the fastest, but it is the one most likely to already be in your procurement system.

Telnyx has the cleanest API and the most boring documentation, which is a compliment. Their Call Control primitives map cleanly to the kind of state machine you actually want to build for an agent. Twilio's TwiML, by contrast, is a legacy XML format that was designed before voice agents were a category, and it shows.

The compliance bit, briefly

Dutch outbound calling sits under the Telecommunicatiewet and the AVG (Dutch GDPR). Two practical implications for an automated agent.

First, the Bel-me-niet Register. You are legally required to scrub against it for B2C calls. None of the three carriers do this for you. We use a daily diff against the official register and reject any number that appears. The carriers will route the call regardless. The fine for ignoring this lives in the tens of thousands of euros per incident, so do not skip it.

Second, call recording disclosure. Dutch law requires both-party consent for recording. Our agent opens with a Dutch sentence that names the company, states the purpose, and asks if recording is okay. If the answer is no, the recording stops and the transcription continues in memory only. All three carriers support per-call recording toggles via the API. Twilio's is the most granular, Telnyx's is the cleanest to wire up, Vonage's requires a separate webhook configuration that we tripped over twice.

What we actually recommend

For a Dutch-only outbound workload at any meaningful volume, Telnyx is the answer until something changes. The price gap is too large to ignore, the porting experience is meaningfully better, and the API is the one you will resent the least at 11pm on a Thursday when something is broken.

For a workload that is half voice and half something else (SMS, WhatsApp, identity), Vonage's bundling probably wins on total cost of ownership even though the per-minute rate is higher.

For a workload where audio latency is the make-or-break (think: voice agent that interrupts naturally, or sub-second tool calls happening mid-conversation), Twilio is still the safe choice. You will pay for it.

When we built the voice agent for the solar maintenance client on AI agents infrastructure, the thing we ran into was that the cheapest carrier on paper had a 47ms latency penalty that made the agent sound just barely off, and we ended up routing high-intent callbacks through Twilio and cold dials through Telnyx based on a confidence score.

If you are deciding today: pick one number from one carrier, port it once before you scale, and time the port. The carrier whose porting team answers your email in Dutch within two business days is the carrier you want underneath a production voice agent.