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Telephony and VoIP

Managed VoIP (Voice over IP) from On Telecom allows customers to make calls over an Internet connection by using Session Initiation Protocol (SIP) Trunking.

The On telecom Technical Design team are available to help design, plan and rollout VoIP solutions and SIP deployment to ensure that our customers received the solution that fits their business requirements.


  • Free calls between company sites
  • Simplified infrastructure. With VoIP on your network you no longer need separate cabling for your telephone system.
  • Scalable. Traditional PABX (Private Automatic Branch Exchange) based phone systems come in many size ranges and it may be necessary periodically to scrap existing systems and replace hardware; this is not the case with VoIP systems.
  • Reduce operating costs. Because a VoIP exchange is based on software rather than hardware, it is easier to alter and maintain.
  • Improve productivity. VoIP treats voice as if it were any other kind of data, so users can attach documents to voice messages or participate in virtual meetings using shared data and videoconferencing.
  • Flexibility. A Virtual Private Network (VPN) is an allocated amount of bandwidth on the public Internet where public access is prevented through encryption. If your company has its own VPN and combines it with VoIP, you can set up a fully functioning office anywhere there is a broadband connection.

How does VoIP work?

As the diagram below shows VoIP calls can be made via IP Phones, Analogue Phones (via VoIP gateway or VoIP phone adaptor or using SIP or Soft phones over an IP connection using SIP trunking).

VoIP Diagram


If your PBX is not compatible then don't worry! You may be able to upgrade it or On Telecom provide a range of IP enabled PBX's. You will also need a broadband connection, On Telecom can provide standard or preferably a QoS enabled connection that will guarantee voice quality. We can also provide Leased lines and Ethernet products as an alternative for larger projects to create a Managed WAN.

SIP trunking

SIP provides channels over the IP connection which are similar to phone lines or channels of ISDN. Eg. 8 SIP trunks is equivalent to 8 channels of ISDN.

With your SIP enabled PBX and internet connectivity in place, then the cost will simply be the rental of your SIP channels on a monthly basis.

For example: If you currently have 5 ISDN lines that means you can support 5 concurrent calls so you will need to rent.

5 SIP Channels

Call rates will be allocated depending on your predicted call spend. On Telecom VoIP call rates are typically the same as our PSTN rates. Please speak to your Account Manager regarding call rates and SIP trunk rental charges.