Monthly Archives: January 2015

5 ways SIP trunking could halve your phone bill

SIP Trunking will save your business money by replacing old, inflexible and expensive technology like ISDN 30 lines. This article lists all the benefits of SIP trunking along with some considerations that should be taken into account before jumping in.

Save money with a Skywire SIP trunk

SIP trunks can half the cost of ISDN lines


First of all some SIP providers do not charge a monthly rental fees (We are one of them :) ). Compare this to the monthly cost of a ISDN 30 from BT and this alone could halve your phone bill. Second are the low call rates.

SIP trunks route calls across the internet for as much as the distance as possible and only connect to the standard telephone networks at each end of the call. The internet portion of these calls are free.

Your phone numbers will not be fixed to your SIP trunk like DDIs can be fixed to ISDN 30 lines. This means you can swap your numbers and SIP trunks when needed. This can be very useful when moving office or building disaster recovery solutions.


SIP Trunks do not suffer from the same limitations as ISDN 30 lines when it comes to channels. As the name implies ISDN 30 lines are limited to 30 channels meaning you can only have 30 active calls at any one time. In a busy office or small call center this limit will be reached very easily. SIP trunks are only limited on concurrent calls by the speed and bandwidth of your internet connection. This means you will not need to pay for more channels as your company grows.

This does mean your internet connection needs to be able serve your demands. A broadband connection will only be able to deal with a few calls at once but a dedicated leased line is capable of sustaining 100s of calls at once.


To use ISDN an ISDN line would need to be physically installed into your building incurring an installation fee and taking time. A SIP trunk will use your internet connection so there is no need for any specialised connection or installation.

One thing to remember is that if your internet connection fails your SIP trunk will also fail. Some people believe this to be a disadvantage of SIP trunks, but to have any resilient connection you need a backup and it makes much more sense to backup one connection that serves all your needs than to have a backup for two separate connections (Internet and ISDN). One connection from one provider with one backup is going to be much cheaper than the alternative.


Reporting is notoriously difficult to get for ISDN 30 lines. Often these reports are only available weeks after the calls have taken place. Your phone system may record the calls it is programmed to route but it’s reporting may not indicate calls to numbers that have not been programmed (This can be due to bad configuration or the accidental removal of number details in the phone system)

Not having up-to-date records of your calls can cost you big as it may take you much longer to notice configuration errors or misuse of your phone system.

SIP providers should be able to provide you with very recent call stats (Ours is at the most 1 hour behind)

Disaster Recovery / Flexibility

SIP Trunking makes diverting calls to alternate routes very easy. Phone systems can be configured to load balance their calls across two SIP trunks or to prefer one and only use a backup SIP trunk if the preferred trunk fails. This can be done with ISDN lines but the inflexibility of ISDN lines is in presenting the same number from both lines. When you fail over to your backup line you will want your calls to be presented with the same number to your customers.  It is possible for two SIP trunks to present the same number but check with your supplier first.

These features of SIP trunks make office moves simple as two SIP trunks can be setup in both physical locations in the same way and calls can be switched over instantly.

Don’t forget a second internet connection is needed to route SIP calls via another route.


To see how much Skywire Communications can save your company with our unlimited, flexible and cost effective SIP trunks read more here