Adding an AI agent to an existing business line is usually as simple as turning on call-forwarding—no port‑out headaches, no downtime, and you keep the number everyone already knows. Below is a concise guide that covers the core call‑routing concepts you need to understand, plus step‑by‑step methods for the three most common phone setups: smartphone, land‑line, and PBX/VoIP.

1. Key Call‑Forwarding Concepts

Forward‑All vs. Forward‑When‑Unanswered

Tip: For most businesses, forward‑when‑unanswered strikes the best balance—humans get a chance, but the AI agent provides guaranteed coverage.

Ring Strategy: Single, Simultaneous Group, or Sequential List

1. Single extension/number – One target.
2. Simultaneous ring group – Multiple targets ring together; the first to pick up wins.
3. Sequential (hunt) list – Numbers ring one after another in the order you specify.

**Place the AI agent last in a sequential list.** If you drop it into a simultaneous ring group, it will answer immediately every time, preventing humans from ever picking up.

Caller‑ID Pass‑Through

Make sure your forwarding method passes the original caller’s number, not your own. The AI agent can then recognize returning callers and retrieve prior context. Most PBXs and mobile carriers call this “Caller ID pass‑through,” “P‑Asserted‑ID,” or “Diversion header.” Enable it wherever you configure forwarding.

2. Implementation Methods

A. Smartphone

*Star codes vary slightly (T‑Mobile, AT&T, Verizon). Dial *#21# to see current status; ##21# clears it.

Testing checklist:

1. Call from another phone.
2. Verify your mobile still shows the caller’s number when the AI answers.
3. Disable forwarding when finished testing.

B. Traditional Land Line (POTS)

Some regional telcos use *68/*69 instead. Always listen for the confirmation tone and place a test call.

C. PBX / VoIP / Cloud Phone System

1. Locate call‑routing or dial‑plan screen. Vendors label this “Incoming Rules,” “Time Conditions,” “Ring Group,” or “Call Queue.”
2. Create or edit a hunt list (a list of DIDs/Extensions to dial sequentially):
   example:

• Extension 100 – Front desk (0–15 s)
• Extension 101 – Sales group (16–30 s)
• AI Agent – External number (31 s onward)

3. Enable original Caller‑ID on trunk:

• SIP: Send From or P‑Asserted‑ID header unaltered.
• Analog gateway: Turn off “Caller ID transform” or “Mask Caller ID.”

4. Apply & test. Watch real‑time logs; you should see the call flow step through the hunt order.

Got IVRs? Simply point the timeout or “zero‑operator” option to the AI agent’s number.

3. Final Checklist

• Decide forward‑all vs. forward‑when‑unanswered.
• If using a hunt list, put AI agent last, as it always picks up every call..
• Pass original Caller ID end‑to‑end.
• Test after‑hours and during business hours (when lines are busy) to catch edge cases.
• Document the star codes or dial‑plan edits so staff can disable/modify quickly.

With these settings in place, your AI phone agent will pick up when humans can’t—without yanking your number away from its existing carrier. A five‑minute configuration now saves countless missed calls later.