A Rufumleitung AI receptionist setup lets you keep the German mobile number your customers already know. Plenty of small businesses in Germany run on one. It's on the website, the Google profile and the van, and it lives on a prepaid SIM such as ALDI TALK or a contract SIM from a reseller like sim.de. You can keep that number and still have an AI receptionist answer the calls you can't take. The tool is the one your phone already has: Rufumleitung, call forwarding.
This guide covers the German specifics: why a mobile SIM can only be connected through forwarding, which number to forward to, what you need to verify a German local number, the dial codes, costs, and how to test it. For forwarding in general, with UK and US codes, see our call forwarding setup guide.
How a Rufumleitung AI receptionist setup works
Your customer dials your mobile number as usual. Your mobile network receives the call and, depending on the rule you set, either rings your phone or passes the call to another number. If that other number belongs to your AI receptionist, the assistant answers with your greeting, answers questions from what you've taught it, and can book appointments.
The caller doesn't hear a transfer message. They dialled you, and someone picked up.
Two things follow from this:
- Forwarding is a setting on your SIM, not on the AI. You switch it on and off with your mobile network, by dial code or in your phone's settings.
- The forwarded part of the call is your outgoing call. Your network connects the caller onward from your number, and that onward leg is billed to you as if you'd rung the destination yourself, unless your tariff includes it. More on cost below.
Which ways of connecting work with a mobile SIM
Klugon has three ways to connect a phone number. With a German mobile SIM, only one of them applies.
| Option | Works with a prepaid or contract SIM? | Why |
|---|---|---|
| Forward your existing number | Yes | Your SIM forwards calls to a number Klugon gives you |
| Bring your own over a SIP trunk | No | A mobile SIM has no SIP connection to point at us. This option is for business phone systems and VoIP lines, on the voice Business plan |
| Moving the number over (porting) | No | Klugon doesn't support number porting |
So the plan is: get a Klugon number, then forward your mobile to it.
Choose a German number to forward to
The number you forward to should be in Germany. Forwarding to a number abroad is billed as an international call on your SIM, and some tariffs block it altogether. A German destination keeps the onward leg a domestic call.
On the Phone numbers page in your dashboard, open Forward your existing number, choose Germany, and pick a number. You'll see the price before you confirm: each number is $9 a month, billed as its own monthly subscription that you'll find on the Billing page. A voice plan is needed first; plans start at $99 a month with 1,000 minutes, and the pricing page shows how many numbers each tier includes. You can get the number during your trial; it's charged when you buy it.
German local numbers need a local connection
German local numbers (Ortsnetzrufnummern) belong to an area code, and the Bundesnetzagentur requires that link to the area to be respected when a number is handed out; the rules are set out in its Verfügung 25/2006 on local numbers. In practice, before a German local number can take calls, the business has to show it really is in that area.
So pick a number in the area code where your business actually is. A Munich bakery should choose an 089 number, not one in Erfurt (0361) because it looked nicer in the list.
Verify the number: what you'll be asked for
After you get a German local number, its card on the Phone numbers page shows Pending verification and a form listing what's needed. For a German local number, expect these six items:
- Contact details: the contact person's name, the business name, and a phone number, on one line. For example: Contact: Anna Weber | Business: Bäckerei Weber | Phone: +49 89 1234567.
- Proof of local address: a bank statement, utility bill, tax letter or official letter from the last 90 days, showing your name or business name and the local address. Leases and rental agreements aren't accepted.
- ID or company registration: a colour copy of a valid German ID card or passport, or the German company registration certificate.
- The BNetzA registration form: the regulator's form confirming your connection to the area, completed and signed.
- An address inside the area code: the street, number, postcode and city, which must be in the area the number belongs to.
- Company registration number: your Handelsregister number, such as HRB 123456 or Amtsgericht München HRB 123456. Enter N/A for personal use.
Each item shows a short example, and What's accepted opens the full rules. Upload PDF, JPG or PNG files of up to 10 MB, then select Send for verification. The details go to the phone regulator's checks automatically; you don't need to send them anywhere else.
While the details are checked, the number is already charged and its card shows each item as being checked, approved or not accepted. If something isn't accepted, the reason is shown and you can replace just that item. Once everything is approved, the number switches on and its card shows Forwarding set up. Don't leave it late: the order has a deadline, and if the details don't arrive in time it's cancelled.
Set up the Rufumleitung on your phone
Once the Klugon number's card shows Forwarding set up, set the forwarding on the SIM whose number your customers call. German networks use the standard GSM codes. Dial the code with the full Klugon number in international format, then press call:
| Forward | Code | Cancel |
|---|---|---|
| Every call (unconditional) | **21*+49…# | ##21# |
| If you don't answer within 20 seconds | **61*+49…**20# | ##61# |
| When you're on another call | **67*+49…# | ##67# |
| When your phone is off or has no signal | **62*+49…# | ##62# |
| Turn off every forwarding rule | ##002# |
The no-answer delay can usually be set between 5 and 30 seconds in steps of five. To see what's currently set, dial *#21#, *#61#, *#67# or *#62#. Most phones also have a menu for this: on iPhone it's Settings, then Phone, then Call Forwarding (which only offers forwarding of every call); on Android, open the Phone app's settings and look for Call forwarding.
Which rules to use
- You want to keep taking calls yourself: use no answer, busy and unreachable. Your phone rings first; the AI receptionist catches the rest.
- You never get to the phone during the day: forward every call.
- Only after hours: forward every call at closing time and cancel it in the morning. The assistant answers whenever a call reaches its number, so the forwarding rule decides when it's on duty. Our after-hours answering service page covers this setup.
Watch out for your mailbox
On many German SIMs, the network mailbox is already set as the forwarding target for no answer, busy and unreachable. Setting a new rule with the codes above replaces it. If your mailbox still picks up first, it's usually because its delay is shorter than yours; set the no-answer rule again with the delay you want.
What forwarding costs on a German SIM
There are two costs to keep apart:
- Klugon: $9 a month for the number, plus your voice plan's minutes for the calls the assistant handles.
- Your mobile network: setting up and cancelling forwarding is normally free, but the onward leg of each forwarded call is billed like a call from your phone to the Klugon number. With an Allnet flat that includes calls to German numbers, that's usually covered. On a prepaid SIM without a package, expect a per-minute charge. teltarif.de's guide to Rufumleitung explains how networks charge for it.
Some prepaid tariffs only allow forwarding to the mailbox, not to another number. If a code is refused or calls still land in your mailbox, ask your provider whether forwarding to other numbers is included. We can't see your tariff, so check it in your network's price list or customer app before you forward every call. Forwarding to a number abroad is where costs climb fastest, which is one more reason to forward to a German number.
Test it before your customers do
Test from another phone, never from the one you're forwarding:
- Every call: ring your mobile number. The AI should answer and your phone shouldn't ring.
- No answer: let it ring and count the seconds until the assistant picks up. If your mailbox answers instead, see the section above.
- Busy: ring while your mobile is on another call.
- Unreachable: switch your phone to flight mode and ring it.
On each test call, check that the greeting names your business, ask a common question, and try a booking. The call should show up in your inbox afterwards. If a caller asks for a person, the assistant takes their details and flags the conversation for your team; it doesn't put the call through to you. Our article on AI receptionist handover to staff explains how to follow up quickly.
Frequently asked questions
Can I connect an ALDI TALK or sim.de number to an AI receptionist?
Yes, by call forwarding. Keep the SIM, get a German number from Klugon, and forward the SIM's calls to it with the codes above. The SIM itself can't be plugged in, because a mobile SIM has no SIP connection.
Does the Klugon number have to be in my area code?
For a German local number, yes in practice: the verification checks your address against the number's area. Choose the area code where your business is.
Can I start before the verification is approved?
You can set up and test the assistant in your browser straight away. Forwarding calls to the new number only works once the number is approved and active, so leave the Rufumleitung off until its card shows Forwarding set up.
Is my number charged while it's being verified?
Yes. The $9 monthly charge starts when you get the number and continues until you release it, including while it's pending or if the details aren't accepted.
Will my customers notice the forwarding?
No. They call your usual number and hear your assistant's greeting.
How do I turn it off?
Dial ##002# on the forwarded phone. All forwarding rules are removed and your phone rings as before.
Forwarding a German mobile to an AI receptionist takes ten minutes with the codes and a few days for the number's verification, so start with the number. Get your German number on the Phone numbers page, teach the assistant your hours and services with our guide on what to teach your AI receptionist, and write a greeting that names your business. If you haven't signed up yet, Klugon's AI receptionist has a 7-day trial, and the German AI phone assistant page explains it in German.