AI phone assistant explained: how it works, cost, rules

What an AI phone assistant is and how it works

An AI phone assistant is a program that answers calls and talks to callers. Unlike an answering machine, it does not just listen but asks questions: who is calling, what is it about, when would an appointment suit? And unlike an old phone menu with ‘press 1’, it holds natural conversations in full sentences, according to IONOS.

Technically, three building blocks can work together. OpenAI describes this chain in its developer documentation: first, speech recognition turns what is said into text. Then a language model, the same kind of AI as behind ChatGPT, decides what happens next, such as asking a follow-up question, checking the calendar or forwarding the call. Finally, speech output reads the answer aloud in a synthetic voice. According to OpenAI, there are also systems in which a single model understands speech directly and speaks itself.

You usually do not need a new number for the assistant to receive your calls. With IONOS and HalloPetra, according to the providers, you set up call forwarding from your existing number to a number provided by the service. IONOS says you decide yourself when the assistant steps in. After each call you usually get a summary, with IONOS for example by email with the caller's number and request.

What it can do and where its limits are

Typical tasks are appointment requests, callback requests and answers to common questions, for example about opening hours or services. IONOS lists filtering and forwarding calls and answering based on documents you upload; appointment booking is included from its mid-range plan. fonio advertises that the assistant, once connected to your calendar, checks free slots and enters appointments.

Mittelstand-Digital Zentrum Hamburg, a government-funded advice centre for small businesses, supported the introduction of such an assistant at a hearing aid business. According to its report, the team could hold consultations without interruption, and requests arrived already sorted. As drawbacks, the report names the effort of setting up and training the assistant, because the AI has to tell the business's technical terms apart reliably, the care needed with data protection, and that customers only accept the assistant if the voice is clear and sounds natural.

The most important limit: a language model can be wrong. The Datenschutzkonferenz, the body of Germany's data protection authorities, says the results of AI applications must be questioned critically and points out that language model providers themselves state that the texts they produce make no claim to be correct. On the phone this means the AI can mishear a name, mix up a house number or give wrong information. For emergencies such as water damage, IONOS says the assistant can recognise keywords like ‘emergency’ or ‘water damage’ and forward the call straight to an emergency number you have set. But that only works if you set up these rules and someone answers that number.

Our assessment: strong dialects, building site noise or a poor mobile connection can make speech recognition worse. We found no reliable figures on this for German dialects. Test the assistant with your own calls before going live. By the way, an AI chatbot on your website or on WhatsApp works on the same principle, just without speech recognition and speech output; fonio sells the two as separate products.

What an AI phone assistant costs: three pricing models

Providers bill in very different ways. Three examples from providers on the German market with published prices (checked on 18 October 2026):

Per call: IONOS charges 39 euros a month on its Flex plan with 30 calls, then 0.49 euros per call. Flex Pro costs 69 euros with 100 calls and appointment booking, then 0.39 euros per call. All-Flat Advanced costs 99 euros with all calls included. Prices include VAT. According to IONOS, all three plans can be cancelled monthly; the small print, however, notes that offers partly depend on minimum contract terms. With this model, the length of a call makes no difference.

Minute allowance: fonio, a provider based in Vienna, charges 119 euros a month on its Solo plan when paying monthly, or 99 euros a month when paying yearly. This includes 1,000 minutes and one phone number, and only one call can run at a time. The Team plan costs 359 or 299 euros with 3,600 minutes and three simultaneous calls. Once the minutes are used up, fonio automatically adds packs of 100 minutes for 15 euros. All prices exclude VAT.

Monthly package by business size: HalloPetra, a provider aimed at tradespeople, charges 99 euros a month for sole traders, 199 euros for businesses with 1 to 10 employees and 499 euros for 10 to 50 employees. A minute allowance is included. Every started minute counts as a full minute, and extra minutes cost 0.20 to 0.30 euros depending on the plan. The pricing page does not say whether prices include VAT. According to the provider, the monthly plan has no minimum term.

Our calculation for a small business with 80 calls a month: with IONOS Flex that would be 39 euros plus 50 times 0.49 euros, a total of 63.50 euros including VAT. With fonio Solo it would stay at 119 euros plus VAT as long as the 1,000 minutes are enough. When comparing, look at VAT, contract term, billing per call or per started minute, and what happens when the allowance runs out.

Which rules apply in Germany and the EU

Telling callers it is an AI: Article 50 of the EU AI Act has applied since 2 August 2026. Under paragraph 1, providers must design AI systems that interact directly with people so that those people are informed they are dealing with an AI, unless this is obvious. According to the European Commission, people must be notified clearly and distinguishably from the start of the first interaction. By its wording, the obligation is addressed to the provider, meaning the company that develops and offers the assistant. Our assessment: still check that the announcement at the start is switched on. On the phone, a natural-sounding AI voice is rarely obviously an AI.

Recording: under Section 201 of the German Criminal Code, anyone who without authorisation makes an audio recording of another person's privately spoken words commits an offence. In 2018, the Datenschutzkonferenz resolved that recording phone calls is, as a rule, only permitted with the consent of the other party. The caller must be asked before recording starts and must actively agree, for example by saying yes or pressing a key. Merely offering a way to object and then carrying on with the call is not enough. Whether a service records at all varies: IONOS says calls are processed only briefly in working memory, no audio is stored and only a text summary remains. HalloPetra says it stores audio and transcripts encrypted on servers in Frankfurt. So ask before you start.

Data protection: if your business uses an AI service from an external provider, the Datenschutzkonferenz says this is often processing on your behalf, which requires a data processing agreement with the provider under Article 28 GDPR. The Munich Chamber of Commerce (IHK München) also points to the information duties under Articles 13 and 14 GDPR and the entry in your record of processing activities. The law firm IT-Recht Kanzlei recommends a separate page on your website with privacy information about the phone assistant.

This page is not legal advice. For questions about your own situation, your chamber of crafts, chamber of commerce or a data protection adviser can help.

Example: a morning at a heating company

Here is how it can look in everyday life. The example is made up but typical: a heating engineer with four staff is out at two building sites in the morning, and nobody is in the office. He has set calls to go to the AI assistant when nobody picks up.

At 8:10, a customer calls because her heating has gone cold. The assistant answers with the company name and says that an AI is speaking. It asks for the address, the type of heating and whether any water is leaking. Because she says no, it takes a callback request and confirms it. Shortly afterwards, a property manager reports water in the basement. That keyword is set up as an emergency, so the assistant forwards the call straight to the master craftsman's mobile. A third caller only wants to know whether the company also installs heat pumps. The assistant answers that from the documents it has been given.

At lunchtime, the master craftsman reads the summaries on his phone. The customer's house number was misheard; he notices when he calls her back. That is exactly why control stays with you: the assistant takes over answering the phone, not the responsibility.