SIP Trunks


If you want to get rid of costly ISDN line rental fees and make your voice system more agile and flexible, but don’t want to get rid of equipment that’s still fit-for-purpose, SIP Trunking is the answer.

Our cloud-based SIP Trunking service provides an IP connection from your existing PBX infrastructure, allowing you to make calls over your data connection. This gives you all the benefits of IP voice, such as advanced call handling and routing, without replacing your entire phone system. ISDN line rental expenses are removed, and you’re also getting more out of your data connection.

Call routing changes can be made instantly using the online portal which offers intuitive, point-and-click number management, and lets you deploy cloud-hosted services such as voicemail, call recording and automated IVR services.


  • Access cloud-based VoIP (voice over IP) telephony without replacing your existing equipment
  • Cut out ISDN line rental costs; capitalise on your existing data connections and use them for voice traffic.
  • Gain total control over your number management and call routing functions in the cloud.
  • Minimal capital expenditure: simply pay for what you use.
  • Value-added services such as affordable cloud-based call recording and 
IVR services.
  • No need to rent spare phone lines just in case you need them; add 
additional SIP trunks as and when required.
  • SIP trunks ensure you benefit from future developments in IP voice. By building communications and business strategies based around the advanced features of hosted telephony, you guarantee that any future investments in IP are easy to integrate, minimising disruption to your business.

Technical features

VoIP and PSTN Connectivity

The THUS platform provides you with full VoIP switching and routing capabilities, plus connectivity to the mainstream PSTN, to all mobile operators, and to other SIP phone users. This enables business-grade VoIP calls to be made and received over SIP trunks, while bringing you all of the benefits and flexibility of IP Voice.

SIP Gateway

Calls come into IP-PBX over data connection; for traditional PBXs, a SIP gateway converts VoIP to TDM.

THUS Service Portal

Administer your SIP trunking routing and related services from a single, easy-use portal.

Number Flexibility

Map inbound DDIs (direct dial-in) to SIP trunks using a simple web-based interface. Map multiple geographic and non-geographic numbers to your SIP trunks.

Whisper Prompting

Whisper prompting provides the B-party with a short audio prompt prior to connecting the caller. Use this, for example, to confirm the caller’s location, number dialled or service selected.

Alternate Routing

Define alternate routing for each DDI and change the current routing, as required, with just the click of your mouse. This is perfect for disaster recovery scenarios, when inbound calls must be rerouted to other sites, home numbers or mobile phones.

Shared Infrastructure

Use one data connection for all your voice and data traffic.

PCI-Compliant Call Recording

Whether your business needs to comply with regulations, follow in-house quality assurance, or train its staff, Call Recording stores your calls so you can manage them in a structured, organised fashion. The THUS Service Portal provides access to all recordings. You can download or stream to a PC, organise into folders, annotate and rate for various uses, and rename or delete as required.

Access Methods

Depending on your bandwidth requirements, your data connection can be implemented using any of the following access methods:

  • Dedicated Internet Access (DIA) via broadband or Ethernet
  • THUS Multi Protocol Label Switching (MPLS) IP-VPN data link


Can I still deploy SIP Trunking if I have a legacy (non-IP) PBX?

Yes. The only difference between an IP PBX and non-IP PBX deployment of SIP Trunking is that legacy PBX require a SIP to TDM converter. We provide a simple gateway to serve this purpose.

How will SIP Trunking reduce my connectivity costs?

Delivering voice over IP eliminates the need for a traditional phone circuit. Instead of paying for two networks, you need only pay for one.

If I have procured different PBXs for different times, will SIP Trunking work across all of them?

Whether IP or TDM, and regardless of which vendor you purchased your PBX from, SIP Trunking can unify your entire telephony estate, working with whatever solution you already have in place.

How can I plan a road-map to a fully IP-enabled estate without throwing out systems which are still fit-for-purpose?

As old systems go end-of-life, Hosted IP Voice can be deployed to replace some platforms while SIP Trunking brings all sites within a single manageable framework.

Will I get the same QoS across SIP as I would with traditional voice circuits?

Yes, in fact, better. The service platform’s 99.999% resilience, dual-sited redundant architecture and built-in secondary routing capabilities can provide much stronger guaranteed service levels than any TDM connection.