Setting up call forwarding: the four routes and their pitfalls

First: the three kinds of forwarding

Whichever route you take, you decide when calls are forwarded:

Most businesses combine them: delayed, plus when busy, plus when unreachable. Everything stays as it was; only voicemail is replaced.

Route 1: GSM key codes on a mobile

The fastest route, and it works on any handset regardless of make or network. You type the codes like a phone number and press call (<target> = your assistant's number):

iPhone and Android also offer forwarding in their settings — the same network features sit behind those switches. Either way the forwarding then lives in the network, not on the handset: it still applies when the phone is off.

Pitfall — cost: depending on the tariff, the forwarded leg of the call is paid by the line owner. At Telekom, forwarding on mobile costs the same as a normal call on the tariff; on o2 contract tariffs it is typically €0.29 per minute to other networks and landlines (price list, as of 8 July 2026), and o2 Prepaid only forwards to the mailbox. At o2, then, a call flat rate does not automatically cover forwarding. Check your provider's price list before forwarding permanently.

Route 2: network-side forwarding at your telephony provider

Here forwarding is set up at your provider rather than on the device. Which route the providers describe for this differs (as of 2 November 2026):

• Telekom: in the Telefoniecenter, for landline connections. For mobile, Telekom names only key codes and device settings.
• 1&1: in the Control-Center, for the landline connection. For the mobile number, 1&1 names only the GSM codes.
• o2: in the Mein o2 app, for mobile.
• Vodafone: no portal route described. For landline and cable, Vodafone gives key codes, typed on the phone connected to the router.

Advantages:

• Independent of the router: immediate forwarding, or forwarding for "unreachable", stored at the provider still applies when the router or phone system is off or faulty — unlike a rule in a FRITZ!Box (route 3)
• No codes: you click the forwarding together instead of typing codes
• Times and rules can sometimes be managed in the portal

For landline numbers this is the recommended standard route, where the provider offers it. The steps for each provider are in separate guides: "Setting up call forwarding at Telekom", "Setting up call forwarding at Vodafone", "Setting up call forwarding with o2" and "Setting up call forwarding with 1&1"; rules in the router are covered in "Setting up call forwarding on the FRITZ!Box".

Route 3: through the phone system

Businesses with their own PBX or a cloud phone system set forwarding up as a rule inside it: "if extension X does not answer within 20 seconds → external number Y." Advantages: managed centrally, time-controlled (opening-hours profiles), and different per extension. The FRITZ!Box in a small office can do this too (call handling → forward to an external number). Here the device itself forwards the call by setting up a second call to the destination.

Pitfall — caller ID (CLIP): if your provider's network does the forwarding (key code, app, customer portal — routes 1 and 2), the standard has the destination receive the caller's number. Your own number typically arrives only when a FRITZ!Box or phone system forwards the call itself — that is, on this route, if your provider does not allow the caller's number to be passed on. Then an assistant cannot capture the caller's number automatically. Check it after setting up, with a call from a second phone.

Route 4: direct SIP connection

For larger setups, some providers also wire their assistant into your telephony as its own destination over a SIP trunk — which does away with classic forwarding entirely and lets caller data through cleanly. This is a project for your IT provider rather than a five-minute setup, and it pays off once call volume is significant or you have several sites. Not every provider offers it — ask beforehand. scoco.ai offers no SIP trunk: it is connected by forwarding only, via routes 1 to 3.

Which route for whom?

• A tradesperson with a company mobile: route 1, delayed plus when busy plus when unreachable — done in two minutes
• A business with a landline number: route 2 at the provider — more stable than a rule in the router
• An office with a (cloud) phone system: route 3, as a rule inside the system
• Several sites or high volume: route 4, with your IT partner — at providers that offer it (with scoco.ai: route 2 or 3)

scoco.ai is deliberately built for this standard: you keep your number, a forwarding rule is all it takes, and your phone system needs no rebuild. Basic setup takes about 10 minutes. A planner in the dashboard shows the right codes, with your scoco number already filled in.