Glossary
Number porting
Number porting means taking an existing phone number along from one telephone provider to another.
This entry describes the situation in Germany, where keeping your number when switching providers is governed by the Telecommunications Act (Telekommunikationsgesetz, TKG). The new provider submits the porting request, and the previous one releases the number on an agreed date. The details of the line holder have to match exactly. Geographic numbers stay tied to their area code. Other countries have their own rules and procedures.
For an AI phone assistant, porting is rarely necessary. Call forwarding or a SIP trunk is usually enough, and the existing contract stays unchanged. Porting is worthwhile when the whole line is moving anyway. It takes longer than forwarding and cannot be reversed at short notice, so plan a date outside peak hours.
In practice
This describes the procedure in Germany. If you port, the order runs through the new provider. You fill in a porting form with name and address exactly as they are held by the current provider; even a different company suffix can lead to a rejection. Clarify beforehand what happens to further numbers on the same line, whether an internet contract depends on it and who cancels the current contract. Often the new provider does that together with the porting. Your provider will tell you the exact steps and deadlines.
An example
A driving school moves office and switches from an old landline to a cloud phone system at the same time. The number is printed on the cars, so it has to stay. The new provider requests the porting for a Tuesday morning in the school holidays. Until then the old line keeps running. The school had been using its phone assistant for weeks by way of call forwarding; after the porting it only sets up the forwarding again in the new system.
A common misunderstanding
Many people believe the number has to move to the assistant’s provider before an AI phone assistant can be used. In most cases forwarding is enough. The second misconception concerns speed: porting is not a switch you flip the same afternoon. And anyone who cancels first and wants to port afterwards risks, in an unfavourable case, that the number can no longer be taken along. So have the new provider confirm the order of the steps.
At Call0
You do not have to change your number for Call0: you forward it or use a Call0 number.
Source: Section 59 of the German Telecommunications Act (TKG), in German
This entry explains the general principle, with a focus on German and EU law, and is not legal advice. For your case, the text of the law and the advice of a qualified professional apply.
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As of: 12 October 2026