Fourstack builds AI voice agents, agentic workflows, WhatsApp campaign systems, and compliance automation — answering every call, chasing every renewal, and closing the loop inside your own systems. Scoped in a week. Live in six.
No retainer to start · Fixed-scope pilot · You own the code
| Call | Intent | Dur | Score |
|---|---|---|---|
| #48219 | Book demo | 2:14 | 0.94 |
| #48218 | Renewal | 1:38 | 0.91 |
| #48217 | Support | 4:02 | 0.88 |
| #48216 | Book demo | 1:55 | 0.96 |
| #48215 | Pricing | 0:47 | 0.72 |
Built on the stack your team already trusts
Voice is where most clients start, but the same team ships the compliance engine, the WhatsApp campaigns, and the back-office automation behind it. Most agencies stop at the prototype — we ship the retries, the evals, the fallbacks, and the handover doc too.
Agents that pick up on the first ring, hold a real conversation in the caller's language, act inside your CRM mid-call, and escalate to a human with full context. Inbound and outbound, on your existing telephony.
Multi-step agents that plan, call your tools, and finish the job — refunds processed, tickets triaged, quotes generated, records written back. Guardrailed, observable, and cheap to run.
Automated campaigns and two-way conversational flows on the WhatsApp Business API — broadcast, segment, follow up, and let an AI agent handle every reply instead of a shared inbox.
Systems that read every document, call, and submission against your rulebook — KYC packets, vendor contracts, audit evidence, call-recording conduct — and flag the exceptions with the clause they breached.
The document-shaped, spreadsheet-shaped work that eats your week. Invoices, onboarding packets, reconciliation, data entry — parsed, validated, and pushed into the systems of record.
RAG over your contracts, SOPs, tickets, and product docs — answering in chat, on WhatsApp, or inside the tools your team already has open, with citations they can actually check.
Regression suites, traced runs, and cost dashboards so quality is measured, not assumed.
The unglamorous plumbing between your CRM, billing, telephony, ERP, and warehouse.
Internal copilots and customer-facing AI features, built to your spec and shipped under your brand.
An embedded pod of engineers when you need velocity without a headcount req.
Missed calls are the most expensive leak in a services business. Our voice agents answer on the first ring, hold a real conversation in the caller's own language, act inside your CRM mid-call, and escalate to a human with the full context attached. They run on Vox, our own platform — so you can take the keys whenever you want them.
Voices and languages, per agent
Realtime engine choices
Coverage, every hour they call
Inbound · +91 80 4718 2200
Sales line · Indore
Hi — I'm calling about the quote you sent last week.
Of course. I've got your file open — the ₹1,84,000 quote from the 4th. Would you like to move ahead, or adjust the scope?
Adjust it. Can we drop the onboarding add-on?
Done — that brings it to ₹1,52,000. I've booked Priya to confirm on Thursday at 3pm and emailed you the revised PDF.
Screening candidates and chasing an overdue EMI are the same problem wearing different clothes: a high-volume conversation with a script, a system of record, and an exception path. We build the agent once and retarget it.
Calls every applicant within minutes of the CV landing, runs the screening script, checks notice period, location, and salary expectation, scores the fit, and books the panel slot straight into the recruiter's calendar.
Pre-due reminders, EMI follow-ups, and soft-bucket recovery at a scale a tele-calling floor can't reach. Captures promise-to-pay, offers pre-approved settlements, and routes disputes to a human agent.
Answers on the first ring, resolves the L1 questions outright — order status, balance, policy details, working hours — and hands the rest to a person with the transcript and account already open.
Calls a new enquiry back in under a minute while intent is still hot, qualifies against your criteria, and books the sales team only on the leads that clear the bar.
Books, confirms, reschedules, and reminds — clinics, diagnostics, service centres, salons, field visits. Cuts no-shows by calling the day before instead of sending an SMS nobody reads.
Renewal nudges, lapse recovery, claim-status updates, and document chasing — the repetitive policy-servicing calls that eat an operations team's entire month.
Delivery confirmation, address correction, failed-attempt reattempts, COD verification, and driver coordination — outbound at volume, with the exceptions pushed to your ops desk.
Post-service calls that actually get answered, in the customer's own language, with open-ended answers transcribed and themed instead of reduced to a 1-to-5 tap.
Enquiry follow-up for institutes and edtech — course details, fee structure, eligibility, campus visits — calling every lead in the list instead of the top 10% a human team can reach.
One voice per language, selectable per agent.
Other providers are an integration we scope with you.
Not on the list? The build is the same either way — tell us the call your team is tired of making.
Get a demo numberVox is our own voice-AI platform. Describe a phone agent in the browser, ground it in your documents, and test-call it on your own phone before a customer ever hears it. Every completed call comes back as a transcript and a webhook into your systems.
Run it yourself, or have our team build and operate it for you. Same platform either way — which is why we can move quickly and why nothing about your setup is a black box.
Voices and languages
Realtime engine choices
Telephony dialers
Speaks
A deliberately short loop. If a workflow can’t prove itself in six weeks, it probably shouldn’t be your first one.
Week 1
We sit with the team doing the work, watch the actual process, and score every candidate workflow on volume, error cost, and system access. You get a ranked backlog and a fixed-price pilot scope — whether or not you hire us.
Weeks 2–4
One workflow, built end to end and put in front of real traffic behind a human gate. Nothing is theoretical: it reads your data, writes to your systems, and gets measured against the manual baseline from day one.
Weeks 5–6
Eval suites on real transcripts, retries and fallbacks on every tool call, cost ceilings, PII handling, and a traced run log your team can read. This is the step most agencies skip and most pilots die on.
Ongoing
Roll to the next workflow, or take the keys. Repos, prompts, evals, and runbooks are yours from the first commit — we write the handover doc either way. No lock-in, no black boxes.
Every engagement is built so you could fire us and keep running.
AI work goes wrong when the vendor holds the keys. We treat the handover as the deliverable — the system belongs to your team, documented well enough that your own engineers can extend it without calling us.
A recruitment screening agent and a loan-recovery campaign are not the same job, so they don't carry the same price. We quote each use case after a week of mapping — a fixed number, before any build starts.
One use case, mapped and shipped to production. Priced as a single fixed number once we've seen the process — no hourly meter, no scope creep.
per use case
A standing team shipping use case after use case at your cadence. Sized to the pod you need, not the hours we log.
rolling, 30 days' notice
We run it as a service — regulated data, VPC or on-prem deployment, procurement paperwork, and an SLA behind it.
annual, per volume
So the quote isn’t a surprise when it lands.
Send us the use case and we’ll come back with a fixed number and a date — usually inside a week, and free either way.
Get a scoped quoteModel and telephony usage billed at cost, passed through with no markup. All quotes exclusive of GST.
If yours isn’t here, ask it live — we answer this stuff straight.
Six weeks from the first call for a first workflow: one week mapping, two to three weeks building against real traffic behind a human gate, then two weeks hardening. Simple internal automations often land sooner; anything touching regulated data or a slow procurement cycle takes longer, and we will say so during mapping rather than after.
No. Most of the work in a real deployment is exactly the messy-data plumbing — parsing the inconsistent exports, reconciling the two systems that disagree, handling the records with missing fields. If you have an engineering team we will work alongside them and hand over as we go; if you don’t, we cover it.
It stays in your accounts. We build inside your cloud and your vendor contracts wherever possible, use zero-retention API endpoints by default, and redact PII before anything reaches a model unless you’ve explicitly approved otherwise. For regulated workloads we deploy into your VPC or on-prem.
It sounds like a competent person on a slightly compressed line. The things that break the illusion are latency and interruption handling, not voice quality — so we tune hard for fast first response and native barge-in, and the agent says it is an AI assistant when asked. It transfers to a human the moment the conversation leaves its scope.
Everything ships behind guardrails sized to the blast radius. Low-stakes actions run autonomously; anything that moves money, sends external mail, or changes a contract sits behind a human approval step until the eval numbers earn it autonomy. Every run is traced, so when something is wrong you can see exactly which step did it.
Vox dials through Smartflo or Twilio today, selectable per call, and you keep your own numbers and carrier contract on either. If you are on a different provider, that is an integration we scope as part of the deployment rather than something that works on day one — we will tell you which it is on the first call. If you have no telephony yet, we provision it.
It is allowed on the WhatsApp Business API within Meta's rules, and staying inside those rules is part of the build. That means opted-in recipients, approved message templates, correct category selection, and respecting the 24-hour service window. We monitor quality rating and pacing so your number doesn't get throttled — mass unsolicited blasting is the thing that gets senders banned, and we won't build it.
The rulebook is data, not code. Policies, clauses, and thresholds live in a versioned source your compliance team edits directly, and every finding cites the rule version it was judged against — so when a regulation changes you update the rule and re-run, rather than waiting on an engineering release. Findings stay reviewable: the system flags and evidences exceptions, a human signs them off.
No. Code, prompts, eval sets, and infrastructure live in your repositories and accounts from the first commit, and the handover document is part of the pilot deliverable — not an upsell. Monthly pods run month to month with 30 days’ notice.
Yes. We work across IST-overlapping and US-overlapping hours and bill in INR or USD. Most delivery is async with two live calls a week.
One post per use case: the arithmetic for sizing it before you commit, how we build it, and where the honest limits are.
Most teams track cost per lead and never track the leads that never reached a human. Here's the arithmetic for putting a number on your unanswered calls.
Time-to-first-contact is the most under-managed number in hiring. What changes when screening calls stop being rationed by recruiter hours.
Early-bucket recovery is a volume problem that tele-calling floors cannot solve economically. What shifts when contact attempts stop being rationed — and where the compliance line sits.
Twenty minutes, no deck. Bring one workflow you’d like to hand over — a phone line, a compliance check, a WhatsApp campaign — and we’ll tell you honestly whether it’s a good first candidate, and roughly what it would cost.