Conditional call forwarding has been around since the 80s. The idea is simple: tell your phone to forward a call somewhere else only under specific conditions — usually when your line is busy or when you don't answer within a few rings. The calls you actually pick up never get forwarded.
That's the mechanic that makes "AI receptionist" practical. You don't have to give up your number or hand all your calls to a robot. You just point the calls you'd otherwise miss at something useful.
This is the reference for how to do that on every major US carrier and the most common VoIP providers. The destination is whatever AI answering service you're using — for the rest of this article I'll write it as {number}, which represents the forwarding number your AI service gives you.
Star codes by mobile carrier
| Carrier | Forward when busy | Forward when unanswered | Cancel |
|---|---|---|---|
| Verizon | *71{number} | (same code, single trigger) | *73 |
| AT&T | *90{number}# | *92{number}# | #21# |
| T-Mobile | **67*{number}# | **61*{number}# | ##21# |
Notes:
- Verizon uses one star code that covers both busy and no-answer. After dialing, wait for the confirmation tone before hanging up.
- AT&T uses two separate codes. Dial each one and wait for the success message after each.
- T-Mobile also supports a configurable ring delay —
**61*{number}*10#waits 10 seconds before forwarding. Default is around 15 seconds.
For per-carrier setup walkthroughs (with the full FAQ for each), see:
What if you're on VoIP
VoIP providers don't use star codes (mostly). You set forwarding in the admin dashboard. The exact menu path varies, but every major provider supports conditional forwarding. Look for "Call Handling," "Call Forwarding," or "Call Flow" in your admin. The rules you want are usually labeled "Forward when busy," "Forward when unanswered," or "Forward missed calls."
The six VoIP providers most often used by small service businesses each have a slightly different path:
- RingCentral → Settings → Phone → Call handling → "Forward missed calls"
- Nextiva → Users → Voice Settings → Forwarding (three conditions: unanswered, busy, unreachable)
- Ooma → My Ooma → Preferences → Call Forwarding (also: uncheck "Require key press on answer")
- Grasshopper → Extensions → Edit → Add forwarding number
- Quo → Settings → Phone Numbers → Call Flow → "If no one answers" fallback
- Comcast Business → Voice settings → Call Forwarding (or use star codes
*71/*90)
Per-provider walkthroughs with the gotchas (Ooma's key-press setting, Nextiva's Answer Confirmation, Comcast's Be Anywhere) are at the supported phone providers index.
What if your carrier isn't in the table
Almost every business carrier in the US supports conditional call forwarding in some form. The main exception is Google Voice, which doesn't support forward-on-busy or forward-on-no-answer the way a regular carrier does. If Google Voice is your business line, you'd need to port the number to a supported carrier first.
For everything else: dial *#62# from your phone to query its current forwarding state, or check your carrier's support docs for "conditional call forwarding." The feature is almost always there, just sometimes under a different name.
Common gotchas
A few things that quietly break otherwise-correct setups:
- Wrong code for the carrier. AT&T's
*92does not work on T-Mobile. Mobile-network forwarding codes are carrier-specific, even when they look similar. - Forwarding to a number that won't answer. If your AI service's forwarding number rings out without picking up, the original call eventually drops or rolls to voicemail at your AI service's level. Test by calling your own number from another phone and not picking up — you should hear the AI greeting within a few rings.
- Ring count too short. If you set forwarding to trigger on 1 ring, you'll never have time to answer calls yourself. 4 rings (about 15–20 seconds) is a typical default.
- Answer Confirmation enabled (VoIP). Several VoIP providers (Nextiva, Comcast, Ooma) default to asking the destination to press a key to accept the call. AI services can't press keys. Disable that option.
Where the calls go
Once forwarding is set up, the question is what answers the call. CallSaver is one option — it's an AI receptionist that's tuned for service-business calls (HVAC, plumbing, electrical, contractors), captures caller name and reason for call, and routes a callback request into a queue your team works.
For the full list of providers we work with, plus per-provider setup walkthroughs, see supported phone providers. Or book a 15-minute call if you want to talk through the right setup for your specific stack.