Every AI receptionist platform hits the same fork early. Should each business customer get its own dedicated phone number, or should calls arrive on shared numbers and be sorted out by software? And if a business already has a number its customers know, should the platform forward it, port it, or ignore it?
The short answer: give every tenant at least one dedicated DID, even if their public number stays where it is. The dedicated number is what lets your platform know, reliably and instantly, whose receptionist should answer. How customers reach that number (forwarding, porting or publishing it directly) is a second decision, and the right answer changes as the tenant matures.
Here’s the comparison in full, with a scorecard and a decision rule at the end.
The four options
AI receptionist platforms typically choose between four ways to get a business’s calls to the agent.
A. Dedicated new DID, published. The platform provisions a fresh number for the tenant, and the business puts it on its website and listings. Simple and clean, but the business has to change the number its customers know.
B. Forward the existing number to a dedicated DID. The business keeps its current number with its current provider and sets call forwarding (always, or on busy or no answer) to a DID the platform provisioned for that tenant.
C. Port the existing number in. The business moves its number to the platform’s provider. The platform then controls routing entirely.
D. Shared numbers with software routing. A small set of numbers serves many tenants, and the platform identifies the tenant from the caller, a menu choice, or forwarding headers.
Why option D loses
Option D looks efficient on a spreadsheet and fails in practice. It’s worth dismissing first because it shapes everything else.
The problem is identification. If several businesses forward their calls to the same shared number, the platform has to work out which business the caller was trying to reach. In principle, forwarded calls can carry headers indicating the originally dialed number, such as Diversion or History-Info. In practice, whether those headers survive depends on the business’s phone provider, the carriers in between and how forwarding was configured. Sometimes they arrive; sometimes they don’t; sometimes they arrive malformed.
When identification fails, the AI answers as the wrong business, or as no business at all. For a receptionist product, there’s no worse first impression. A menu (“press 1 for Smith Dental”) fixes identification by destroying the experience you’re selling.
A dedicated DID per tenant eliminates the problem. The called number is the tenant. No header parsing, no guessing.
The scorecard
Scoring options A, B and C on the factors that matter for a receptionist product (higher is better, 1 to 3):
| Factor | A. New DID, published | B. Forward to dedicated DID | C. Port in |
|---|---|---|---|
| Speed to go live | 3 | 3 | 1 |
| Business keeps its known number | 1 | 3 | 3 |
| Reliable tenant identification | 3 | 3 | 3 |
| Caller ID reaches the agent | 3 | 2 | 3 |
| Platform controls routing and failover | 3 | 2 | 3 |
| Easy for the business to undo | 2 | 3 | 1 |
| Supports SMS on the public number | 3 | 1 | 3 |
A few scores need explanation.
Caller ID on forwarded calls (B: 2). Most forwarding delivers the original caller’s number, but some provider setups replace it with the business’s own number. Test with the tenant’s actual provider before promising caller recognition.
Routing control on forwarding (B: 2). If the business’s current provider has an outage, forwarding stops, and your platform can’t fix it. You also depend on the business not accidentally disabling forwarding.
SMS on the public number (B: 1). Forwarding moves calls, not texts. If callers text the business’s main number, those messages still go to the old provider, not your platform.
Undo (C: 1). Porting back out is possible but slow, which makes businesses cautious about committing on day one.
The decision rule
Put the scorecard together and a clear pattern emerges.
Start with B, built on a dedicated DID. Most small businesses want to try an AI receptionist without changing anything customers see. Forwarding their existing number to a tenant-specific DID gets them live in minutes, keeps their number, and is trivially reversible. Because the forwarding target is dedicated, identification is reliable from the first call.
Offer C once the tenant is committed. When the business has used the product for a while and wants SMS on its main number, better failover or one less vendor, move them to porting. Our guide to porting numbers with LOA and FOC explains what the business will need to provide.
Use A for new lines. A new location, a campaign-specific line or a business without an existing number: provision and publish a fresh DID.
Never build on D.
Option B has one operational requirement that’s easy to miss: when a tenant churns, their forwarding DID goes into quarantine before reassignment, because the business may not remove the forwarding promptly. Otherwise, the next tenant’s receptionist will start answering the previous tenant’s customers. Our guide to multi-tenant DID inventory covers quarantine and number lifecycle in detail.
Beyond the number: what else the tenant’s DID needs
Choosing the number model is the first step. A few further details decide whether the receptionist feels professional.
Concurrency
A business number can receive several calls at once, especially at opening time or after a promotion. Make sure the DID and the path to your platform support the concurrency your agent can handle, and decide what happens on the call that exceeds it: queue, voicemail or overflow to a human.
Handoff to a human
Receptionists escalate. When the AI transfers a caller to the business owner’s mobile, you’re usually either sending a SIP REFER (if the upstream supports it) or bridging an outbound leg. Bridging means you pay for an outbound call as well as the inbound one, so price it in. Decide what caller ID the owner sees on the transferred call: the original caller’s number is most useful, if your routes can present it.
Outbound callbacks
Many receptionists also call people back: confirming appointments, returning missed calls. Presenting the business’s own number on those calls needs authorization from the business and a route that delivers the caller ID intact. It also brings in the answer-rate issues covered in our post on AI outbound answer rates, including attestation and spam labeling.
Text follow-ups
If the receptionist sends appointment confirmations by SMS, the sending number needs messaging capability, and in the US, local numbers used for business texting generally need 10DLC registration per business. That’s another reason committed tenants tend to port: it puts calls and texts on one number.
Testing a new tenant before go-live
A receptionist tenant should be tested end to end before the business points real customers at it. The checks that catch most problems:
Call the dedicated DID directly and confirm the agent answers as the right business, in the right language, with the right greeting. Then set up forwarding from the business’s number and call that number from an outside mobile, confirming the call arrives and the caller’s number reaches the agent. Test the busy and no-answer forwarding conditions separately if the business uses them, because they’re configured separately on most phone systems. Trigger a handoff to a human and check what caller ID the owner sees. Finally, send a follow-up text if the product does that, and confirm it arrives from the number the business expects.
Record the results against the tenant. When something breaks later, knowing that forwarding worked on day one narrows the search.
Moving a tenant from forwarding to porting
The move from option B to option C is where platforms often cause their own outages. The tenant is already live on forwarding, so the port has to happen without breaking a working setup.
Keep the forwarding DID active throughout. Configure routing for the business’s main number on your platform before the port date, pointing at the same agent and tenant as the forwarding DID. When the port completes, calls to the main number arrive directly; any calls still arriving through forwarding, because a line wasn’t reconfigured or a secondary number still forwards, keep working. Only after both paths have been verified should you retire the forwarding DID, and then through quarantine rather than immediate reuse.
Tell the business what changes for them. They’ll need to remove forwarding settings with their old provider eventually, update anything that texts from the main number, and stop paying for the old line once the port is confirmed.
Where the connectivity layer fits
This post covers the number decision. The layer underneath, SIP trunking into your media servers, codecs, latency and scaling, is covered in our SIP trunking for AI agents hub and our guide to building an AI calling platform.
On the number side, coverage determines how quickly you can serve businesses in new markets. IDT Express provides DID numbers in 140+ countries, so a receptionist platform can offer dedicated forwarding DIDs to tenants across most of its target markets through one provider. For fundamentals, see our guide to DID numbers.
Frequently asked questions
Does each AI receptionist customer need its own phone number?
Yes, in practice. A dedicated DID per business lets the platform identify which business a call is for from the dialed number alone, which is far more reliable than inferring it from forwarding headers on a shared number.
Can a business keep its existing number with an AI receptionist?
Yes. The business can forward its existing number to a dedicated DID provided by the platform, or port the number to the platform’s provider. Forwarding is faster and easier to reverse; porting gives the platform full control, including SMS.
Why not use one shared number for many businesses?
Forwarded calls don’t reliably carry the originally dialed number, so a shared number can’t consistently tell which business the caller wanted. When identification fails, the AI answers as the wrong business.
Does call forwarding pass the caller’s number to the AI receptionist?
Usually, but not always. Some provider setups replace the caller’s number with the business’s own number on forwarded calls, so it’s worth testing with each business’s provider.
What happens to a forwarding number when a customer leaves?
It should be quarantined before reassignment, because the former customer may keep forwarding calls to it for some time. Reassigning it immediately would send one business’s callers to another business’s receptionist.
Build on dedicated numbers
Building an AI receptionist product? Explore IDT Express SIP trunking for AI agents and in-market DID numbers for your tenants.
