Using SIP Trunks as an ISDN replacement
We have had quite a few customers recently comparing the cost and quality of ISDN vs using a combination of SIP trunks and SHDSL, so we thought we would run a comparison for cost using a ISDN 30 as the high end benchmark and 2 x ISDN 2 as the low end benchmark.
REPLACE ISDN 102030 WITH SIP TRUNKS
An ISDN 30 PRI Line rental would be typically around the $900 mark and comes with the carrier installation, fixed at 30 channels (it can be varied to 10 or 20 channels), and carrier call pricing which would be around 20 - 35% higher than typical SIP Trunking call charges.
Using a 2mb/2mb SHDSL connection (this should carry 30+ calls) the cost would be, depending on carrier selected, between $350 and $599 and the cost of 30 SIP trunks would be $300 so over all, the rental is similar or within $150 per month if using a budget carrier. Note budget services will not provide the full advertised bandwidth so call quality may suffer during peak times.
So why consider using SIP Trunking as an ISDN replacement? The main difference is flexibility. The SIP trunks can be added or removed as required depending on workload and call volume. SIP trunks can be added and removed with a phone call with next to no lead time. A 2Mb/2Mb service can carry up to 40 channels. SHDSL comes with substantially lower installation costs than ISDN and that would remain as the only contracted portion of the service.
So overall it may be a borderline decision Replacing ISDN 30 with SIP trunks until greater penetration of SHDSL leads to price reductions for SHDSL. However if your business needs on demand flexibility in the number of channels required for call volumes then SHDSL should be the choice.
When it comes to call charges there is no comparison ... SIP Trunking with un timed national calls, no flag fall on calls to mobiles and flat rate locals calls makes SIP Trunks around 20 - 35% lower.
REPLACE ISDN 2 WITH SIP TRUNKS
Substituting SIP trunks for ISDN 2 may be a simpler and more cost effective solution. With an ISDN line rental being around $75 per month we will use for the exercise 2 X ISDN 2 services.
To replace 4 channels of ISDN only requires an ADSL service and 4 channels can easily be run on a ADSL connection shared between Voice & Data...meaning because most business already have an ADSL connection there is no added cost for running 4 SIP trunks over the ADSL connection.
With the cost for 4 Sip trunks being around $50 vs $150 for 2 X ISDN 2 it seems to be a no brainer to use SIP trunking as a substitute for ISDN 2 and gains the benefit of significantly greater flexibility with the capacity to take SIP trunks up or down in 2 channel increments at any time.
The only limitation is with existing PBX equipment the customer will need to get ATAs (typically $100 per channel) and possible card changes to the phone system to make SIP trunks work. Of course if starting out new equipment can be ordered ready to go.