DID and virtual numbers in India for AI calling

A DID (direct inward dialling) number is a phone number that rings straight through to your system over a trunk, with no switchboard in between. A virtual number is one that is not tied to a physical line or a SIM. For AI calling you need two kinds of number. The one buyers ring can be any ordinary local, mobile-format or toll-free number. The one your outbound calls come from is regulated: as of September 2026, TRAI wants promotional calls from the 140 series, and service or transactional calls from 1600 (banks, financial firms and government) or 1601 (other sectors, phased in). This is not legal advice.

What DID and virtual numbers are

Old office switchboards had a few external lines and many internal extensions. DID gave each extension its own public number, so a caller could reach a desk directly. On a SIP trunk the idea is the same without the hardware: the carrier maps a number to your trunk, and every call to that number arrives at your gateway as a SIP INVITE naming the number that was dialled.

A virtual number is the broader idea: a number that lives in the carrier's network rather than on a SIM or a copper pair. Every DID number on a SIP trunk is virtual in that sense. For an AI voice agent, the terminology matters less than two practical tests. The number must reach your gateway as a SIP call, and your outbound calls must be allowed to present it.

One detail catches everyone. The same handset can appear in different forms depending on which way the call went. In our own logs the same buyer showed up as ten digits on an inbound call and with the country code on an outbound one, 9820134567 in one place and +919820134567 in the other. Compare those as full strings and they are two different people. We compare numbers on their last ten digits, the part that identifies an Indian subscriber.

Which number series is used for what

The Department of Telecommunications assigns number series, and TRAI's regulations say which calls must come from which series. As of September 2026:

140: promotional calls

TRAI's clarification of 10 July 2026 says it "has mandated use of 140xx series numbers for making promotional calls by entities of any sector", and that an entity wanting one must register with a telecom operator under the TCCCPR framework.

The same note explains the buyer's side. Customers can block promotional calls from 140 numbers, sector by sector, on the DND registry, and a customer who has blocked a sector will not receive 140 calls from it. Real estate is its own category in the preference schedule of the February 2025 regulations (PDF), opens in a new tab, so a buyer can block property calls and still receive, say, calls from their bank. Tagging or filtering of 140 calls is not allowed except through that registry, and TRAI's September 2026 amendments (PDF), opens in a new tab spell out that call-management apps may not blanket-block, filter or spam-tag the designated series, though each person can still block calls on their own phone.

1600 and 1601: service and transactional calls

The 1600 series was assigned by DoT, in TRAI's words, "for allocation to entities in the Banking, Financial Services and Insurance (BFSI) sector, and Government organisations to clearly distinguish their service and transactional calls from other commercial communications." TRAI's direction of 19 November 2025 set deadlines for adoption running from 1 January to 15 March 2026 for banks, NBFCs, mutual funds, stockbrokers and pension entities.

On 10 August 2026 TRAI began phasing in the 1601 series for service and transactional calls by other sectors, starting with utilities, courier and logistics. Operators must verify eligibility, allocate 1601 numbers directly to eligible entities rather than to intermediaries or aggregators, and complete Phase I onboarding within 90 days. TRAI is explicit that 1601 numbers "shall not be used for promotional voice calls by any entity."

Where a real-estate business sits

A call that sells a flat is a promotional call, and it belongs on the 140 series. As of September 2026, real estate is not in the first phase of 1601, and 1600 is for regulated financial entities and government.

Be careful with mixed calls. The February 2025 regulations define a promotional voice call so that "if promotional content is mixed with any type of commercial Voice Call, such voice call shall be treated as a Promotional Voice Call." A possession update that also pitches a second flat is a promotional call.

Ordinary numbers

TRAI's February 2025 amendments restrict "senders from using normal 10-digit numbers for telemarketing, ensuring that all commercial communications originate from designated headers or specific number series." Running outbound sales calls from a salesperson's mobile, or from an ordinary landline DID, is exactly what this is aimed at.

The number buyers ring

The series rules are about where commercial calls originate. The number printed on your hoarding, portal listing and ad is the one buyers ring you on, and it can be an ordinary number. The choice is about what the buyer sees.

• A local number carries a city code and reads as a local office. It suits a single-city project.
• A toll-free number costs the caller nothing. TRAI's numbering plan recommendations of 6 February 2025 (PDF), opens in a new tab describe the free phone service as one where "the calling party can access this service free of cost, with the called party bearing all expenses", in the format 1800 followed by a service code and number. It suits campaigns that run across several cities.
• A mobile-format virtual number looks familiar to buyers, and works the same way over the trunk.

Whichever you choose, keep it stable. A number that changes between the brochure and the hoarding splits your inbound calls across two places, and old print keeps ringing for years. If you want to know which ad produced which call, ask your vendor whether your setup can map a number to a source tag before you print several.

With an AI voice agent on the line, every call to that number is answered, at 2 pm or 2 am, in the caller's own language, whichever it is.

Getting a number onto an AI agent

The mechanics are covered in our SIP trunking guide. In short:

1. The carrier provisions the number on a trunk pointed at the agent's gateway.
2. You find out, from the carrier, the exact form the number arrives in on an inbound call, and the gateway is configured to claim it in that form.
3. Someone places a real test call to the number and hears the agent answer, with audio both ways.
4. For outbound, the carrier confirms which caller ID your calls will present, and that it is from the series your calls need.
5. Recordings are pointed at the vendor, so every call is kept against its lead.

The second step is where one of our worst connection failures began. A carrier presenting the number in a different format from the one the gateway expects produces a flood of refused calls that looks like an attack.

What a business needs before its first outbound call

Most of this is registration with your telecom operator. No software can do it for you, and it is the client's obligation, not the calling vendor's.

1. Registration as a principal entity on your operator's DLT platform.
2. A registered telemarketer placing the calls, linked to you on DLT.
3. 140-series numbers for promotional calls.
4. A declaration of automated calling. The September 2026 amendments (PDF), opens in a new tab define an A2P call as "a voice call that is initiated by an application, software system, or automated platform without direct human dialling", including autodialling, robo-calls and artificial voice. Every sender must declare A2P use to its originating operator in advance, with the number ranges it will call from, and A2P calls made without that declaration are treated as unsolicited commercial communication. This takes effect sixty days after the amendments are published in the Gazette. An AI voice agent placing calls fits the definition as written. The same amendments introduce a per-minute termination charge on A2P calls between operators, and exempt calls from the 140, 1600 and 1601 series.
5. Scrubbing against the NCPR, the national preference register, through your DLT access, before every campaign.
6. Evidence of the basis for each call. Under the September 2026 amendments, an enquiry used as the basis for commercial calls must be made in writing or by digital means and kept in a verifiable form, and it supports calls for seven days. We cover the practical effect in inbound vs outbound AI calling, and the rules in full in our TCCCPR guide.
7. A suppression list of your own. BlackWolf checks every number against its suppression list before each dial: opt-outs heard on calls, complaints and numbers you add. That list is not the NCPR, and it does not replace step 5. See compliance for exactly what the product enforces.

For the difference between DND, the NCPR and your own list, read DND and NCPR explained. For how all of this fits a property sales team, see AI calling for real estate.

What to do next

Ask your operator three questions in writing: which series your outbound calls will come from, how your trunk links to your DLT registration, and how you declare automated calls under the September 2026 amendments. Do not place a promotional call until all three have answers.