VoIP Access – SIP Trunking

The benefits of traditional Colt telephony, delivered over an IP connection

If you are using an IP PBX then connecting to Colt with IP is a cost-effective solution that unlocks the benefits of convergence for your business. With Colt’s VoIP Access – SIP Trunking, you are connected to our core voice network. This is not consumer-grade internet telephony, with the quality risks that that brings, but business-grade service. Your voice quality is as good as – and often better than - the service you receive on traditional telephone lines

Switching  to an IP-based telephony system helps your business become more productive and competitive. Your employees can stay connected to your network, whether they’re working in the office or away from it.


  • Consistent service delivery across 13 countries
  • Connect directly to Colt via a line from our network into your IP PBX
  • Reduce your overall costs, and management time, with a converged voice and data network
  • Keep your existing numbers
  • Easily scale your telephony system up as your business grows
  • Reduce your calling charges with free calls between sites
  • Supports calls to all destinations, including emergency services

Colt VoIP Access – SIP Trunking eases your migration to a converged, voice and data IP network that connects you to the outside world. VoIP Access – SIP Trunking makes it possible to have an end-to-end IP network by allowing your calls to be routed (over an IP infrastructure) between your premises and the PSTN.

With Colt VoIP Access – SIP Trunking, you don’t have to invest in on-site gateways because we provide this functionality within the Colt network. VoIP traffic is passed between your IP PBX and our network, using one of the two best-known standards-based protocols in the industry: H.323 or SIP (Session Initiation Protocol).

While H.323 has proved a popular choice for use in VoIP networks in recent years, SIP is rapidly gaining popularity, and has been widely backed by major IP PBX equipment vendors including Cisco, Avaya, Aastra and Siemens. Colt lets you choose between these protocols, and will help you make the best decision for your VoIP network. Traffic may be sent between your IP PBX and Colt VoIP Access using either of the popular codecs: G.711 or G.729a. Fax and DTMF are also supported through standards-based protocols. Supplementary services such as Direct Dial In, presentation and restriction of CLI and Call Forward, and also emergency call handling, are part of the service offer.

Colt VoIP Access – SIP Trunking supports multiple access mechanisms, including Colt IP VPN (MPLS) and Internet access. Bandwidth can be scaled up as your voice capacity requirements grow.

Diamond Call Analyser

Diamond Call Analyser is a free to use online web-based service ideal for performing functions such as Telecoms Expense Management. It is available for the following Colt Voice services:

  • Voice Line (including IP Voice Line)
  • Voice Connect
  • VoIP Access (SIP Trunking)
  • IN Services


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