AI Voice Agent Development Service — Built for You

✓ Inbound & outbound ✓ Calendar + CRM connected ✓ Human transfer ✓ Tested on real calls

Quick answer

What is an AI voice agent? 

An AI voice agent is software that holds phone conversations. It converts speech to text, uses a large language model to decide what to say or do, and replies with a natural synthetic voice. It can answer questions, book appointments, qualify leads, take messages and transfer calls to people.

What does this service include? 

Codersarts engineers design the call flow, build the agent on Vapi or Retell, connect your phone number, calendar and CRM, tune voice and latency, set up compliance basics, and test with real calls.

How long and how much? 

Starter from $199 (3 days, one inbound call flow). Standard $399 (5 days, inbound or outbound with booking and CRM logging). Advanced $799 (10 days, multi-flow agent with transfers, analytics and automations). Per-minute running costs are paid to the platform and are separate.

Is this your problem?

• Calls go to voicemail after hours, and those callers don't call back

• Staff spend hours on the same booking, pricing and opening-hours calls

• Leads from ads call in, but nobody qualifies them quickly

• You tried a voice AI demo, but it sounded robotic, laggy or interrupted callers

• The agent can't book into your calendar or update your CRM

• You're unsure what's legally allowed for outbound AI calls

Why voice AI demos fail in real calls

• Latency. Each turn passes through speech-to-text, the LLM and text-to-speech. Voice AI benchmarks treat under about 800 ms as natural. Above roughly 1.5 seconds, callers talk over the agent or hang up.

• Poor turn-taking. The agent cuts callers off, or keeps talking when they interrupt.

• Unclear call flows. Without a designed script and fallback paths, the agent drifts, loops or makes promises it shouldn't.

• No integrations. A voice agent that can't check availability, book, or log the call gives you only a transcript.

• Compliance gaps. In February 2024 the US FCC ruled that AI-generated voices count as "artificial" voices under the TCPA, so many outbound AI calls need prior express consent. Recording and disclosure rules also vary by country and state.

We design the conversation, the integrations and the guardrails, then test on real calls before go-live.

How an AI voice agent works (simple view)

Caller ──► Phone number (Twilio / SIP / platform number)
              ↓
   Speech-to-text  →  LLM (with your instructions, knowledge & tools)  →  Text-to-speech
              ↓                         ↓
       Turn detection           Tools: calendar · CRM · knowledge base · transfer
              ↓
   Call summary + transcript → CRM / email / Sheets / n8n workflow

What we do

1. Scope check: define the use case, caller types, goals, languages, hours and handoff rules.

2. Conversation design: write the greeting, questions, objection handling, fallbacks and when to transfer.

3. Build: configure the agent on Vapi or Retell, choose the LLM and voice, and add your knowledge base.

4. Integrations: connect your phone number, calendar (Google, Outlook, Calendly, Cal.com), CRM (HubSpot, Salesforce, GoHighLevel, Zoho) and automations (n8n, Make, Zapier).

5. Latency & voice tuning: pick fast models and streaming settings, tune interruption handling and voice style.

6. Compliance basics: add an AI disclosure, a recording notice, opt-out handling and a consent field for outbound calls.

7. Testing: run scripted and real test calls, then fix weak answers, loops and transfer issues.

8. Go-live & handover: dashboard access, call-log review guide and tuning tips.

Packages

Add-ons: Priority delivery (+50%) · Extra call flow (+$49) · Additional language (+$49) · CRM integration (+$49) · 30-min walkthrough call (+$25) · 14-day support (+$39)

Setup is a one-time fee. Per-minute running costs (platform, AI model, voice, phone) are billed by the providers. Final scope and price are confirmed after a free 30-minute scope check.

Vapi or Retell: which do we use?

We recommend a platform during the scope check based on your needs:

Typical running cost: independent comparisons put all-in costs in the range of about $0.10–$0.30 per minute, depending on model, voice and telephony. Check current vendor pricing before relying on these figures. We estimate your cost per call during scope.

We can also build on Bland, Synthflow, ElevenLabs Agents, Twilio + OpenAI Realtime or a custom stack when needed.

Use cases

Compliance & safety we build in

• AI disclosure at the start of calls where required or preferred

• Call recording notice and consent handling by region

• Outbound consent: calls only to contacts with recorded consent, plus opt-out handling, in line with FCC/TCPA guidance in the US

• No sensitive data collection unless your provider setup supports it (e.g. HIPAA BAA)

• Guardrails: the agent can't promise refunds, prices or outcomes outside its approved script

• Human transfer for complaints, emergencies and high-value calls

We set up these technical controls. Your legal team should confirm requirements for your industry and region.

What you get

• A live AI voice agent on your phone number

• Call flow and conversation design document

• Calendar, CRM and automation integrations (per package)

• Test call recordings and a fixes log

• A dashboard and call-log review guide

• Proof of done: recorded test calls showing booking, transfer and edge cases

What we need from you

Required (the delivery clock starts once we have these):

• The use case: inbound, outbound, or both

• Your FAQs, scripts, services and pricing information

• A phone number or provider (or we set one up)

• Calendar and CRM access, if booking or logging is included

• Transfer rules: who to call, when, and what hours

• What a successful call looks like (definition of done)

Optional:

• Preferred platform (Vapi or Retell), voice style, accent and languages

• Existing call recordings to learn from

• Industry compliance needs (healthcare, finance)

• Whether you need an NDA

How it works

1. Free scope check (30 min): use case, platform, integrations and package.

2. Design & build: call flow, agent setup and integrations.

3. Test & prove: real test calls, and you hear the results.

4. Go live & review: launch on your number and adjust within your package's revisions.

Why Codersarts Tasks

• One accountable team: a managed Codersarts engineering team builds and tests your agent.

• Conversation design + engineering: scripts, latency, integrations and guardrails together, not just a platform setup.

• Platform-neutral: we pick Vapi, Retell or another stack based on your needs, not a partnership.

• Room to grow: add channels (web chat, WhatsApp), more flows or a full AI support system later.

Related tasks

• Build n8n AI Agent: automate what happens after the call

• Add AI Chatbot to Your Website: the same knowledge, on your site

• Build WhatsApp or Telegram AI Bot

• Build AI Customer Support Agent

• Build Custom GPT or AI Assistant

Bigger than one task? Plan an AI customer-experience build →

FAQ

How much does it cost to build an AI voice agent? Setup starts at $199 for one inbound call flow. Standard ($399) adds calendar booking and CRM logging, and Advanced ($799) adds multi-flow inbound and outbound calls, team transfers and analytics. Per-minute running costs are billed separately by the voice platform and providers.

How much does an AI voice agent cost per minute to run? It depends on the platform, AI model, voice and phone provider. Independent comparisons typically put the all-in cost around $0.10–$0.30 per minute. We estimate your cost per call during the scope check.

Vapi or Retell: which is better? Neither is best for everyone. Vapi suits highly customized, developer-driven agents with flexible providers. Retell suits faster setup for booking and receptionist agents with bundled pricing. We recommend one based on your use case.

Will it sound robotic or laggy? We choose fast models and natural voices, enable streaming and tune interruption handling, targeting under about 800 ms response time, which voice AI benchmarks treat as natural.

Can it book appointments into my calendar? Yes. Standard and Advanced connect Google Calendar, Outlook, Calendly or Cal.com to check availability and book.

Can it transfer calls to a human? Yes. It can take a message for callback, warm-transfer to one number (Standard), or route to different teams by rules (Advanced).

Is it legal to use AI for phone calls? Inbound AI answering is widely used. For outbound calls in the US, the FCC ruled in February 2024 that AI-generated voices fall under TCPA rules, so prior express consent is generally required. We build disclosure, consent and opt-out handling, and your legal team should confirm requirements for your region.

Can it speak multiple languages? Yes. Advanced includes up to 3 languages, and extra languages are available as an add-on.

Can it work with my existing phone number? Usually yes, through call forwarding, SIP or porting, depending on your provider. We confirm this during scope.

Do we own the setup? Yes. The agent runs in your platform account, and you get the call-flow design, prompts and integration details.

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