Do I need to change my phone system? No — and when you do

The normal case: rebuild nothing

An AI phone assistant has its own phone number. You connect it by having your calls forwarded there — by key code on your mobile or in your provider's customer portal; both are carried out by the provider's network. Your number stays, your devices stay, your phone system (if you have one) stays untouched. Switch the forwarding off and everything is as it was — which is what makes getting started risk-free. Note: on a mobile, voicemail is itself a forwarding on no answer. The new forwarding replaces it, and ##002# deletes it too — to get voicemail back, set its forwarding up again. The step-by-step routes are in the basics article "Setting up call forwarding: the four routes and their pitfalls".

This normal case covers more than many people assume: sole traders with a company mobile, practices and offices with a landline number, businesses with a FRITZ!Box — none of them needs any rebuild at all.

Exception 1: a rule in the phone system is more elegant

If you already run a phone system — a classic PBX, a cloud phone system or even just a FRITZ!Box — you can set the forwarding up as a rule inside the system rather than in the network. That is not a rebuild but a line of configuration, and it is worth it if you want more control:

• Different per extension: the workshop extension goes to the assistant after 20 seconds, the boss's extension does not.
• Time profiles: forward immediately outside opening hours, during the day only on no answer.
• Separately per number: treat the office, private and fax numbers differently — the FRITZ!Box, for one, can do this, as "Setting up call forwarding on the FRITZ!Box" shows.

The price for that: the rule lives in your hardware. If the system fails, the forwarding fails with it — the network-side variant is more robust.

Exception 2: a SIP connection at high volume

Above a certain call volume — several lines, several sites, the assistant as a permanent part of your telephony rather than a voicemail replacement — some providers offer an alternative to forwarding: the direct SIP connection. Forwarding still works at that volume; with SIP, though, the assistant is wired into your telephony as its own destination, classic forwarding falls away, and the caller data comes through in full (the CLIP problem of forwarding disappears). Honestly: this is a project with your IT provider, not an afternoon — and not every provider of an AI assistant offers it. The detailed comparison is in "SIP trunk or call forwarding — which connection fits?".

The decision tree in words

1. Do you even have a phone system? No → call forwarding by code or customer portal. Done. No rebuild.
2. You have a system — do you need different rules per extension, number or time of day? No → network-side call forwarding in the customer portal. The system stays untouched. Yes → set a forwarding rule up in the system. Still not a rebuild — a setting.
3. Is the assistant permanently the first point of contact for high volume or several sites? Yes → look into a SIP connection with your IT partner, and ask the assistant's provider whether it offers one at all. That is the only case that smells of a "project".

Pitfalls: where it snags in practice

• Old systems with no maintenance access: when nobody remembers how to configure the PBX from 2009, network-side forwarding in the customer portal is the pragmatic detour — it takes effect before the call ever reaches the system. Just establish which level your phone numbers sit on.
• Duplicate rules: forwarding in the network and in the phone system leads to behaviour that is hard to diagnose. Pick one place, document it.
• Caller ID: if your phone system or FRITZ!Box carries out the forwarding itself, your number rather than the caller's can arrive at the assistant (the CLIP problem) — depending on whether your provider lets the caller's number through. Forwarding in the provider's network generally passes the number on; a test call shows what arrives.
• The cost of the second call leg: depends on the tariff and is not automatically covered by a flat rate — at o2, for example, forwarding from a mobile to a German landline costs €0.29 a minute, even on tariffs such as O2 Free Unlimited (price list, as of 2026-07-08). Worth checking your provider's price list once.

What this means for scoco.ai

scoco.ai is deliberately built for the normal case: you keep your number, a forwarding rule is all it takes, nothing changes on your phone system, and basic setup takes about 10 minutes. Whether the forwarding comes from your mobile, from the portal or from your phone system makes no difference to the assistant — it answers what arrives. scoco.ai does not offer a direct SIP connection: even with your own phone system, the connection is a forwarding rule to the scoco number.