If a voice agent is going to answer the phone, the calls have to reach it. Call forwarding is the whole mechanism: an instruction to the telecom operator about where the call should go.
There are two completely different versions of that job, and the first thing to establish is which one you are in.
First: what kind of number is it?
An ordinary mobile or landline subscription. You control the forwarding yourself from the handset with a keypad code. Take the next section.
A number inside a PBX or business network – Telenor Mobilt Bedriftsnett, Telia Bedriftsnett, Telia Touchpoint, Microsoft Teams Phone, 3CX, Telavox and the like. Here the call hits the operator's platform first, and the platform decides where it goes next. Keypad codes from the handset are either ignored or overridden.
If you are unsure: does the company have a main number that distributes calls to several employees, a voice menu, or an app where staff log in and out of a queue? Then it is a PBX.
Ordinary subscription: the codes
The codes are standardised in the mobile network, which is why they are the same across every Nordic operator. Enter them on the handset keypad and press call.
| What you want | Code |
|---|---|
| Forward all calls | **21*+47XXXXXXXX# |
| Forward only when you don't answer | **61*+47XXXXXXXX**15# |
| Forward when busy | **67*+47XXXXXXXX# |
| Forward when the phone is switched off | **62*+47XXXXXXXX# |
| Cancel everything | ##002# |
| Check what is active | *#21# or *#61# |
The examples use the Norwegian country code; substitute your own (+46 Sweden, +45 Denmark, +358 Finland).
The number in the 61 code is how many seconds the phone should ring before the call moves on. The maximum is 30. We recommend 15 – ring for longer and the caller often hangs up before anyone answers.
Always write the number in international format, with the country code in front. It is the single error behind most “the code doesn't work” tickets. With the country code, forwarding also works while the handset is abroad.
If the phone rejects the code, try two asterisks in front of the number: **21**+47XXXXXXXX#.
Two regional caveats. In Denmark, several operators sell unconditional forwarding as a paid add-on that has to be ordered, and some Danish contracts only permit forwarding to a Danish number. In Finland, forwarding abroad must be set with a plus sign in front of the country code – a regulatory requirement, not a recommendation.
When the company has a PBX
Here you are not setting a code. You are choosing where in the call flow the voice agent goes, and that choice determines how much it takes over.
Outside opening hours. The time-of-day rule sends calls to the voice agent when the office is closed, and to staff otherwise. This is the usual place to start: no risk during staffed hours, and you get real numbers on how many calls actually arrive out of hours. Normally more than people expect.
When the queue can't keep up. The call rings with the staff first. If everyone is busy, or the ring time expires, it moves on to the voice agent instead of to voicemail. Catches the lost calls without changing anything about the answered ones.
As a member of the queue. The voice agent answers alongside the human agents. This requires the number to sit in the queue even though it falls outside the PBX contract. In several platforms that is a separate add-on which has to be ordered and provisioned by the company's PBX administrator, so allow some lead time.
The main number straight to the agent. Full handover. Rarely the right first step – wait until you have seen the numbers from one of the setups above.
As a fallback. The voice agent as a standby, activated when something is down. Note that PBX fallbacks typically stay on until someone switches them off manually, and that the fallback route belongs on the phone number rather than in the supplier contract.
Four traps
Personal forwarding does not catch queue calls. If an employee sets forwarding on their own number, it applies to calls to that number. Calls arriving via the company's queue number keep ringing exactly as before. This is the most common reason a setup looks correct while the agent never receives a call.
One hop at a time. Don't build chains where the call is forwarded twice or three times. Several operators drop the second hop, and the fault is nearly impossible to diagnose afterwards.
Routing loops. If the voice agent needs to transfer to a human, it must transfer to a queue or a direct number – never back to the main number the agent itself sits behind.
Caller ID can be overridden. Queue settings in some PBX platforms can add a prefix or replace the caller's number before the call is transferred. If the agent identifies the customer by number, that quietly stops working without anything looking like an error.
Test before it goes live
Four tests catch almost everything:
- Call from a phone outside the PBX. Internal calls are often routed differently and give false confidence.
- Call when nobody is logged into the queue.
- Call from a withheld number.
- Confirm that the number the voice agent sees matches the number you called from.
And verify what is actually registered in the network rather than what the handset menu shows. *#21# answers that.
Cost and data protection
Forwarded calls are billed by the operator as an ordinary outbound call to the destination number. If the company has unlimited domestic calling, there is usually no extra cost. Forwarding to a foreign number is charged at international rates, even while you are inside the EU/EEA. SMS cannot be forwarded.
When calls are routed to a voice agent, call content and metadata are processed on the company's behalf, which requires a data processing agreement. The caller must also be told they are speaking to AI – an obligation in force since 2 August 2026 – and that belongs in the opening line. Both should be settled before the routing goes into production, not after the pilot.
In short
Ordinary subscription: one code, remember the country code, test from a different phone. PBX: choose a position in the call flow, start outside opening hours, and check whether the calls arrive via a queue number before troubleshooting anything else.
Threll.ai builds voice agents in Norwegian, Swedish and Danish. If you run a PBX, we do this part together with your IT lead – and document the way back to the previous configuration before changing anything.
