Glossary
Call forwarding: how to set it up
Call forwarding automatically redirects incoming calls from one phone number to another number.
There are three common variants: immediately (all calls), when busy, and on no answer after a few seconds. Forwarding is set up with your phone provider, in the phone system or in the router. On mobile networks, and on many landlines in Germany, the standard codes work: **21*target number# for all calls, **67*target number# when busy and **61*target number# on no answer. ##21#, ##67# and ##61# delete the respective forwarding again. Codes on landlines vary by provider and country.
For an AI phone assistant, forwarding is the simplest way to keep the number people already know. You should clarify two points beforehand: whether your provider charges for forwarded calls, and whether the caller’s number is passed on when a call is forwarded.
In practice
Once it is set up, call yourself from a second phone and check three things: does the call arrive at the destination, how many seconds does your own phone ring first, and which number does the other side see? For forwarding on no answer, many providers let you set the waiting time. Choose it so that you can still pick up yourself without leaving callers waiting. Also note where the forwarding was configured. Otherwise someone will later search the phone system for a setting that sits in the provider’s customer portal.
An example
A painting business is reached on the owner’s mobile number. Up on the scaffolding he rarely answers. He sets up forwarding on no answer: if the mobile rings for longer than about twenty seconds, the call goes to the phone assistant. Nothing changes for customers, who dial the number they know. The owner still answers himself when his hands are free, and in the evening he reads who else called.
A common misunderstanding
Forwarding is often confused with porting. With forwarding the number stays with your provider, and you can switch it off again at any time with a code. Voicemail is also overlooked: if it is active, it may take the call before the forwarding applies. And unconditional forwarding of all calls means that your own phone no longer rings at all. To begin with, conditional forwarding is usually the better fit.
At Call0
With Call0 you forward your existing number permanently, only when busy or only outside opening hours. Alternatively, you use a Call0 number.
On this topic:
As of: 12 October 2026