Lines as needed
From 2 lines for incoming and outgoing calls, with additional lines available. This lets you determine how many conversations your AI assistant handles in parallel.
SIP trunk for AI phone assistants
Your phone number, your AI: the SIP trunk for AI phone assistants and voice bots
With DUStel business flex, you connect the real-time engines of OpenAI, Anthropic, and ElevenLabs directly via SIP to your phone numbers. Your AI phone assistant answers calls and makes outbound calls – encrypted, billed to the second, and cancelable monthly.
from €10.02 / month net plus 19% VAT · Term: 1 month
- TLS & SRTP free of charge
- Second-accurate billing
- Term: 1 month
- Network in Germany
Incoming call
via DUStel business flex
- Caller Hello, I would like to reschedule my appointment on Tuesday.
- AI Assistant Sure. Does Thursday at 10:00 AM work for you?
- Caller Yes, perfect.
- AI Assistant Done – you will receive a confirmation shortly.
Technology-agnostic: You choose the AI
DUStel business flex supports the real-time engines and SIP calls of leading voice AI providers. You decide which engine your assistant uses – and you can switch at any time without changing your phone number.
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OpenAI
Real-time engine and SIP calls
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Anthropic
Real-time engine and SIP calls
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ElevenLabs
Real-time engine and SIP calls
Mentioned trademarks are trademarks of their respective owners. No partnership exists.
Three steps to your AI phone assistant
Phone number, SIP trunk, AI engine – that is all your voicebot needs to handle real phone calls.
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Build your tariff
Order DUStel business flex with as many lines and SIP connections as your AI phone assistant needs to handle simultaneously. Port existing phone numbers for free, and add new local phone numbers.
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Connect AI engine via SIP
Connect your SIP connection to your preferred realtime engine. Calls to your phone number are routed to your assistant, and its outgoing calls display your phone number.
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Go live and scale
Your assistant starts making calls from the very first one. If it needs more simultaneous conversations, add more lines – adjustable monthly, with no long-term contract.
You can find the server, port, and TLS settings for your SIP connection in the SIP Setup.
Why DUStel business flex is the right SIP trunk for voice bots
You configure the tariff yourself and pay only for what your AI assistant actually needs.
SIP connections with DDI support
From 2 SIP connections, with DDI support. Extensions can be assigned to specific assistants, departments, or campaigns.
Encrypted via TLS & SRTP
Encrypted signaling and voice – optional and free of charge. Important if your assistant works with customer data.
Billed to the second
Voicebots handle many short calls. With per-second billing, you pay only for the actual call duration.
Port your phone number
Free number porting: Your assistant takes over the number your customers already know.
Combine humans and AI
Call forwarding and group calling, also time-controlled, plus optional IVR menu and ACD system: The AI takes over at night or during peak times, your team during business hours.
D-Flatrates optional
D-Flatrate Landline and D-Flatrate Mobile are optional – for assistants that make many outbound calls.
Monthly billing, postpaid
Contract term of 1 month, billed monthly. Ideal for pilot projects and rollouts that grow quickly.
All options and prices at a glance: DUStel Tariffs and Connection prices.
What your AI phone assistant can do
Reception and customer service
Answer calls around the clock, capture inquiries, answer questions, and transfer to the right team.
Appointments and reservations
Schedule, reschedule, or cancel appointments – without hold music, even on weekends.
Support and tickets
Log faults, clarify follow-up questions, and create tickets before a human needs to take over.
Outgoing calls
Reminders, callbacks, and follow-ups – using your own phone number as the sender.
AI made by dus.net
We use AI ourselves – on our own servers, without cloud AI
dus.net is not just a phone provider for your AI, but also drives AI development in-house. Our Customer Center works with digital employees, and we run the language models behind them on our own hardware in our data center – without US providers, without a third-party cloud.
- AI tools in the Customer Center
- 30+
- Self-service via AI chat
- 24/7
- Data to cloud AI providers
- 0
Sandra & Thomas in the Customer Center
Two digital employees answer inquiries in the Customer Center my.dus.net: Sandra in customer service, and Thomas for technical issues. They look directly into your account instead of a FAQ.
Over thirty tools
The chat checks SIP packets, lifts IP blocks, displays connection records, sets up call forwarding, and creates tickets – in self-service, around the clock.
AI reception by phone
Outside business hours, our digital reception answers – an AI, not a human. It answers questions about credit balance, invoices, connections, tariffs, and outages, and creates a ticket on request.
Confirmation before every change
Our AI does not decide on its own: Every change to the customer account is first presented and only executed after explicit confirmation.
How our AI handles data is described in the Privacy Policy.
Frequently Asked Questions About the AI Phone Assistant with SIP Trunk
A SIP trunk connects your phone numbers to the telephone network via the internet. For an AI phone assistant, it serves as the bridge between the caller and the AI engine: incoming calls are handed over to the engine via SIP, and outgoing calls from the AI run through your connection with dus.net.
DUStel business flex supports the real-time engines and SIP calls from OpenAI, Anthropic, and ElevenLabs. Since the connection runs over the open SIP standard, you remain technology-agnostic and can switch engines without changing your phone number.
This is determined by the number of lines. DUStel business flex starts with 2 lines for incoming and outgoing calls; additional lines can be added for a fee.
Yes. Number porting is free with DUStel business flex. Alternatively, you can order new local phone numbers.
DUStel business flex starts at €10.02 per month, all prices net plus 19% VAT. The contract term is 1 month, and billing is accurate to the second. You can add options such as additional lines, D-Flatrates, or IVR menus as needed.
TLS for signaling and SRTP for audio are optional and free with DUStel business flex.
Die Telefonie läuft über das Netz der dus.net in Deutschland. Die Sprachverarbeitung übernimmt die KI-Engine, die Sie mit Ihrem Anschluss verbinden – es gelten deren Bedingungen. Unsere eigene KI im Kundencenter betreiben wir dagegen ausschließlich auf eigenen Servern, ohne Cloud-KI-Anbieter.
With call forwarding and group calling, including time-based scheduling, as well as the optional IVR menu and ACD system, you can combine AI and your team: for example, the AI outside business hours and your team during the day.
Ready for your AI phone assistant?
Build your DUStel business flex, connect your AI engine via SIP, and go live – cancelable monthly, billed to the second, on the dus.net network in Germany.
Configure business flex nowfrom €10.02 / month net plus 19% VAT · Term: 1 month