• SIP trunking
  • Cloud PBX
  • Virtual numbers

SIP trunks for the phone system you already run.

Khaltrix connects IP PBXs, cloud phone systems and contact-centre platforms to the public telephone network, with inbound numbers, outbound calling and failover routing configured and tested with your team.

  • Compatibility reviewed before you commit
  • IP or registration authentication
  • Tested before go-live

How it connects

Business calls over IP, without changing how your team works.

A SIP trunk replaces physical phone lines between your phone system and the public network. Phones, extensions and menus stay as they are.

Keep your existing PBX

Asterisk, FreePBX, 3CX and other SIP-compliant systems connect without replacing handsets or extensions.

Numbers routed where you need them

Local, national and toll-free numbers delivered to your trunk, PBX or cloud phone system.

Capacity that matches your peaks

Concurrent channels sized to your busiest hour, separate from how many numbers you hold.

How a business call connects

  1. 01
    Your phones and apps Desk phones, softphones and mobile apps register to your phone system as they do today.
  2. 02
    Your PBX routes the call On-site or in the cloud, the PBX applies menus, queues and dial plans.
  3. 03
    The SIP trunk carries it Calls travel between your PBX and our platform over IP, in both directions.
  4. 04
    The network delivers it Carrier interconnects connect the call to mobiles, landlines and international numbers.

Calls in the other direction follow the same path in reverse.

Use cases

One connection, configured for how you use the phone.

Support centres, sales teams, multi-site organisations, resellers and voice applications each need SIP configured differently.

Works with the phone systems businesses already run

  • Asterisk
  • FreePBX
  • 3CX
  • FreeSWITCH
  • FusionPBX
  • Yeastar
  • Grandstream UCM
  • + other SIP-compliant PBXs

Product names are trademarks of their respective owners, listed for compatibility guidance only; no partnership or certification is implied. PBX setup guide

Inbound & outbound

Inbound and outbound calling, planned separately.

The same trunk usually carries both directions, but each raises different questions. We plan each on its own terms.

Professional in a white shirt taking a call on a smartphone

Inbound calling

Callers dial your numbers. The carrier routes each number to your trunk, and your PBX decides what happens next.

  1. A caller dials one of your numbers.
  2. The carrier routes that number to your SIP trunk.
  3. The trunk delivers the call to your PBX.
  4. Your PBX applies its rules: menu, queue or time of day.
  5. The right extension or agent rings.
Virtual numbers
Person in a white shirt dialling a number on a smartphone

Outbound calling

Your PBX applies its dial plan and sends calls to the trunk for delivery, presenting caller ID you are authorised to use.

  1. A user dials a number from their phone or softphone.
  2. The PBX applies its dial plan and caller ID rules.
  3. The call is sent to the trunk, authenticated by IP or credentials.
  4. The carrier network routes the call to its destination.
  5. The destination answers.
SIP trunking

Reliability & security

Resilience and security agreed at setup.

Audio problems, dropped calls and fraud usually trace back to a configuration nobody reviewed. These controls are planned with you before go-live.

  • Inbound failover

    Alternate destinations take over when your PBX is unreachable, agreed and tested before go-live.

  • Fraud controls

    Channel caps, destination restrictions and usage alerts suited to your traffic are agreed during setup.

  • Encrypted calling

    TLS signalling and SRTP media where both your PBX and the route support them.

  • IP restrictions

    IP authentication for static addresses, and firewall guidance to accept SIP only from known sources.

  • Calling permissions

    International and premium-rate destinations are enabled deliberately, never by default.

  • Troubleshooting

    Failed calls are investigated with SIP traces and response codes, and findings are shared with your team.

Read SIP trunking security best practices

Technical capabilities

The technical details your engineers will review.

Each parameter is agreed with your team and recorded on your configuration sheet, so nothing is assumed.

  • Authentication

    IP-based (static public IP allow-list) or SIP registration with digest credentials.

    Confirmed with you: Method per trunk and your public IPs

  • Concurrent channels

    Capacity sized to your peak simultaneous calls, separate from how many numbers you hold.

    Confirmed with you: Channel count and burst needs

  • Transport

    SIP over UDP or TCP, and SIP over TLS for encrypted signalling where supported.

    Confirmed with you: Transport and ports for your PBX

  • Codecs

    G.711 (µ-law / A-law) as the common baseline; G.729 or G.722 depend on route and platform.

    Confirmed with you: Codec order on your PBX

  • DTMF

    Keypad tones sent as RTP events (RFC 4733) so menus and voicemail respond reliably.

    Confirmed with you: Matching method on both sides

  • Media encryption

    SRTP for call audio alongside TLS signalling, when both your PBX and the route support it.

    Confirmed with you: Availability for your deployment

  • NAT and firewall

    SIP ALG, RTP port ranges and public address settings, the usual causes of one-way audio.

    Confirmed with you: Your firewall and router model

  • Redundant routing

    Alternate destinations for inbound calls when your PBX is unreachable; second trunks for outbound.

    Confirmed with you: Failover targets and order

  • Troubleshooting and records

    SIP response codes, call traces and call detail records to diagnose issues and reconcile usage.

    Confirmed with you: Escalation contacts and record access

Why Khaltrix

A careful, documented approach to business voice.

We do not publish unverifiable uptime figures or customer logos. These are the working standards you can expect from the first conversation.

Team meeting around a long conference table
  1. Clear technical scoping

    We ask about your platform, network and call patterns before proposing anything, so the quote reflects what you need.

  2. Compatibility reviewed first

    Unsupported codecs, NAT configuration or outdated PBX firmware are identified before you commit.

  3. Transparent commercial terms

    Channels, numbers, minutes and one-off costs are itemised and explained line by line.

  4. Documented configuration

    You receive the settings your trunk uses, so your team or IT partner can support it with confidence.

  5. Structured testing

    Inbound, outbound, DTMF, caller ID and failover are tested against a written plan before go-live.

  6. Direct technical communication

    You work with people who understand SIP and can discuss your configuration with your engineers.

Deployment

Six steps from first conversation to live calls.

Each step produces something you can review: notes, a configuration sheet and test results.

  1. Step 1: Share your requirements

    Tell us about your phone system, users, numbers, destinations and expected call volumes.

  2. Step 2: Review compatibility and coverage

    We check your PBX and network, and confirm number and route availability.

  3. Step 3: Confirm configuration and terms

    Authentication, codecs, channels, numbers, failover and commercial terms are documented and agreed.

  4. Step 4: Configure the connection

    Your trunk is provisioned and your PBX configured with the agreed settings.

  5. Step 5: Test inbound and outbound

    Inbound to each number, outbound to key destinations, DTMF, caller ID and failover.

  6. Step 6: Go live and review

    Numbers are switched over or ported, live traffic is checked and early issues are reviewed.

City skyline across the water on a clear day

Coverage & numbers

Availability confirmed for your destinations.

Number availability and calling routes vary by country and change with regulation. We confirm coverage for your list rather than publish a map that may be out of date.

  1. 01
    Your request Countries, number types and quantities.
  2. 02
    Availability check What can be supplied for each destination, and the lead time.
  3. 03
    Documentation Proof of address or business registration, where the regulator requires it.
  4. 04
    Provisioning and testing Numbers are routed to your trunk or PBX and inbound calls are tested.

Pricing

Quotes built from your traffic profile.

Instead of a single price list, you receive an itemised quote built from these factors, with every line explained.

  • Concurrent channels

    Simultaneous calls you need, and any burst capacity.

  • Destinations

    Rates differ by country and between mobile and landline.

  • Number rental

    How many numbers, in which countries and of which type.

  • Inbound vs outbound

    Toll-free and some inbound numbers carry per-minute costs.

  • Monthly traffic

    Expected minutes shape metered, bundled or committed pricing.

  • Redundancy

    Second trunks, alternate sites or geographic failover.

  • Integrations

    Work beyond a standard PBX connection, such as a voice application.

  • Compliance

    Number documentation and regional rules that need extra handling.

FAQ

Frequently asked questions.

Short answers here, with longer explanations in our guides.

All frequently asked questions

What is SIP trunking?

A SIP trunk is a voice connection delivered over IP. It links your phone system (an IP PBX or a cloud phone system) to the public telephone network, so calls to and from ordinary phone numbers travel over your internet or private data connection instead of copper or ISDN lines.

Read the full explanation in What is SIP trunking?

Can I keep my existing PBX?

Usually, yes. Most modern IP PBXs support standard SIP trunks. Before anything is ordered we review your platform, software version, network and call-routing needs, so any incompatibility (for example an old PBX without SIP support, or a missing codec) is found up front. Older PBXs can often be connected through a SIP gateway.

What is a SIP channel?

A channel is capacity for one simultaneous call, in either direction. Ten channels let ten calls happen at the same moment, whether inbound, outbound or a mix. Channels are separate from phone numbers: a business with 50 numbers may need only 8 channels if no more than 8 people are ever on external calls at once. See how to estimate channel requirements.

Do I need new IP phones?

Not because of the SIP trunk. The trunk connects to your PBX, not to individual handsets, so the phones registered to your PBX keep working. You only need new devices if you are replacing the PBX itself, for example when moving to a cloud PBX that does not support your current handsets.

Can I receive inbound calls and make outbound calls on the same trunk?

Yes. A SIP trunk normally carries both directions. Inbound calls arrive on the numbers (DIDs) assigned to the trunk and are delivered to your PBX; outbound calls are sent from your PBX to the trunk for delivery to the destination. Whether specific outbound destinations are enabled, and which caller IDs can be presented, is agreed during setup.

How do I request international numbers?

Send us the countries, cities or number types you need (local, national or toll-free) and the quantity. We confirm availability, any documentation the regulator requires (often proof of a local address or business registration), lead time and cost before anything is ordered. Start with a quote request or read about how coverage is confirmed.

How is pricing determined?

Quotes are built from your actual requirements: the number of concurrent channels, the destinations you call, how many numbers you rent and where, the mix of inbound and outbound traffic, expected monthly volume, redundancy needs and any custom integration or compliance work. We explain each line of the quote.

How long does setup take?

It depends on what is involved. Connecting an already-compatible PBX for outbound calling can be quick once terms are agreed. New numbers, regulated countries and number porting add time that is set by number suppliers, regulators and carriers. We give you a realistic timeline for your specific project before you commit, and we test inbound and outbound calling before go-live.

What information is needed for a quote?

  • Your phone system (platform and version) and whether it is on-premises or hosted
  • Peak concurrent calls, or the number of users and how busy they are
  • Countries and number types you need, and whether you are porting numbers
  • Main calling destinations and an estimate of monthly minutes
  • Any redundancy, compliance or integration requirements

Rough numbers are fine. The quote form walks you through them.

What security measures should I consider?

The biggest risk with any SIP connection is toll fraud: someone gaining access to your PBX or credentials and placing expensive calls. Good practice includes IP allow-listing, strong unique SIP credentials, keeping the PBX patched and off the open internet, restricting international and premium destinations you do not need, setting channel and spend limits, and encrypting signalling and media (TLS and SRTP) where supported. See SIP security best practices.

Request a quote

Tell us about your current setup.

Share your phone system, the countries you need and roughly how many calls take place at once. For a detailed request, use the full quote form.

What happens next

  1. 01We review your requirements and your phone system.
  2. 02We ask any clarifying questions about routing, numbers or capacity.
  3. 03You receive compatibility notes, a proposed configuration and an itemised quote.

Services you need (pick all that apply)

Your details are used only to respond to your enquiry. sales@khaltrix.com