An AI voice agent connects to your phone system the same way any other destination does: calls are routed to it, over a carrier forward, a SIP trunk, or a ported number. You do not replace the PBX, change carriers, or rebuild the call flow to run a pilot. The standard pattern is to forward selected call types, such as after-hours calls or one IVR branch, to the agent and port nothing, which keeps the deployment reversible in minutes. SIP trunking comes later, when volume and data passing justify a direct connection, and porting is a commitment most deployments never need. This guide walks through the three connection methods, how the agent sits inside an existing PBX or contact center, how warm transfers to humans work mechanically, how recording and consent are handled, and what happens to the IVR tree you already have.
What are the ways to route calls to a voice agent?
There are three, in increasing order of commitment. Call forwarding is the lightest: your number stays with your carrier and your phone system, and a forwarding rule sends selected calls to the agent's number. Forwards can be conditional, such as after hours, when the line is busy, after a set number of rings, or from one specific menu option, so you choose exactly which slice of traffic the agent sees. SIP trunking is a direct connection: calls travel between your phone infrastructure and the agent platform over the internet using the SIP protocol, carrying audio plus metadata like the dialed number, caller ID, and any data your system attaches. It handles higher volume and enables tighter integration, at the cost of network and firewall setup. Number porting moves ownership of the phone number itself to the agent platform's telephony provider, so calls arrive there natively. Porting takes paperwork and elapsed time measured in weeks, and reversing it takes the same. It is the right tool for a number that exists only for the agent, and the wrong tool for a pilot.
Want this mapped against your own call and claim volume? Book a 30-minute audit
How does a voice agent connect to an existing PBX or contact center?
Mechanically, the agent shows up as one more destination your system already knows how to route to: an external number, a SIP endpoint, or a member of a queue. On a conventional PBX or VoIP system, that means a forwarding rule, a ring-group member, or an extension that points at the agent. On a contact center platform, the agent is typically a transfer target or an entry in the routing flow, placed exactly where a queue or a menu option sits today. This is why deployment does not start with an integration project on the phone side: the routing primitives are the ones your admin already uses. The deeper work is on the other side of the agent, connecting it to the systems where the actual tasks live, such as a scheduling system, a TMS, or a policy admin system, so the call ends in a completed task rather than a message. For what the agent does once the call reaches it, see our overview of AI voice agents.
Flexbone connects this way on purpose, forwarding only the call types an audit has shown to be predictable and leaving the rest of the phone system untouched. See AI voice agents.
Why forward selected call types instead of porting at the pilot stage?
Because forwarding keeps the blast radius small and the exit instant. A forward is scoped: you can send only after-hours calls, only the overflow that currently rings out, or only one branch of the menu, while every other call flows exactly as before. It is reversible: if anything is wrong, the forward comes off in minutes and the system is back to its prior state, with no carrier paperwork involved. And it is honest as an experiment: the agent takes real calls of one type, and the transcripts from those calls tell you whether to widen its scope. Porting at the pilot stage inverts all of this. It puts the entire number's traffic behind the new platform on day one, and unwinding it takes weeks, which turns a trial into a commitment before the evidence exists. In the engagements we run, pilots forward and port nothing; a logistics operation typically starts by forwarding the after-hours check calls and carrier calls that currently go to voicemail, which is traffic nobody is answering today.
See what AI can run at your facility. In a 30-minute audit we map the calls, eligibility, and follow-ups Flexbone can take off your team first.
Book an auditHow does a warm transfer to a human work?
A warm transfer means the agent hands the call to a person with the context attached, instead of just redirecting it. The mechanics: the agent recognizes the call needs a human, tells the caller it is connecting them, and keeps them on the line. It dials the staff member or queue, and before bridging the two, passes what it knows: who is calling, what they asked for, and what has already been verified. That context can arrive as a short spoken summary the staff member hears before the caller is connected, or as text pushed into the system on the staff member's screen. Then the agent bridges the parties and drops off. Compare this with a cold transfer, where the call is simply redirected and the caller starts over from "how can I help you," repeating everything they already told the agent. Warm transfer quality is one of the clearest signals of a mature deployment, because it defines what the worst case feels like: even when the agent cannot resolve the call, the caller loses nothing but a few seconds.
How do call recording and consent work?
Recording happens at the platform level: the audio of the call is captured and transcribed, and the transcript becomes the audit record for what the agent said and did. That record is not optional in practice, because reviewing transcripts is how a team confirms the agent stays inside its scope before widening it. Consent is handled the way call centers have handled it for years: a disclosure at the start of the call stating that the call is recorded, played before the conversation begins. What varies is who must consent. Some US states require consent from one party to the call and others require it from all parties, and rules differ again outside the US, so the disclosure wording, where it plays, and how long recordings are retained are decisions to confirm with your counsel during deployment. The mechanism is straightforward; the obligations attached to it depend on where your callers are. An insurance deployment, for example, typically inherits the carrier's existing recording disclosure and retention policy rather than inventing new ones.
What happens to the existing IVR tree?
It survives longer than people expect, and that is by design. The lowest-risk pattern is coexistence: the existing menu stays in front of callers, and one branch of it, such as "press 2 for scheduling" or the after-hours path, routes to the agent instead of a queue or voicemail. Callers who use the other branches see no change at all. As transcript review shows the agent resolving its branch, more branches move over, and the menu shrinks from the inside. The end state some deployments reach is inversion: the agent answers first, in natural language, and the old tree is kept behind it as a fallback for calls the agent routes rather than resolves. What rarely makes sense is deleting the IVR on day one, because the tree encodes routing knowledge your team spent years building. For a fuller comparison of what the agent does differently from the menu it augments, see voice agents vs IVR.
If you want to map which of your call types could forward to an agent first, and what the transfer paths back to your team would look like, book a call with Flexbone and we will walk through your current routing and where an agent fits without changing it.