ISDN PRI or SIP Trunks? Which is the Best Choice for Your Business?

One of the things I've learned from working in the telecom industry for the better part of a decade is, just as you think you've found a great product everyone will love; something new comes out. One of the products included in this is VOIP SIP trunks, which is a product I have become very familiar with over the past year or so.

For quite some time now, ISDN PRIs were pretty much the only thing on the market for my larger business customers. The fact the circuit provided them with the equivalent of 23 voice lines (and an unlimited number of inbound direct dialed numbers) for a lower cost than having 23 separate lines was always an easy sale for me. But, with VOIP becoming more marketable, the SIP trunk option is one that pops up quite a bit now because, at least for quite a few of my customers, it is an alternative that can save them money.

Which is the right choice for your business? Well, that depends on a lot of factors.

The main advantage of SIP trunks is they provide the same basic services as a PRI but they don't restrict you to the 23 voice channels and this can create a cost savings. For example, if you only really need 15 voice trunks, you can set up that few. Or, if you need 35 trunks, for example, you can have that many without having to pay for a second PRI circuit.

SIP Trunks also usually present a savings when it comes to local or long distance phone calls; often including the calls in the price or connecting them at a significantly reduced price. And, much with other VOIP services, you aren't restricted to a certain phone exchange. You can have a local number or you can have a phone number from another state.

Another advantage to this type of service is it is designed to work with just about every phone system. Unlike an ISDN PRI, which usually requires some sort of upgrade, the SIP trunks can usually be used (with the help of some special equipment) to replace standard phone lines without any major changes.

That being said, SIP trunks aren't always a better option. When doing price comparisons for some of my customers, I have found, in many instances, if they need exactly 23 trunks, an ISDN PRI is comparable in price or, in some cases, even cheaper.

This is especially true when it comes to direct inward dial numbers (DIDs), which can usually be purchased in bulk when using a PRI but are sometimes more expensive with the VOIP alternative; especially since you will often be required to pay extra for 9-1-1 services.

Another disadvantage of this type of service when compared to an ISDN PRI circuit is they do rely heavily on your internet connection and, if you don't have enough bandwidth or are using a public internet connection (DSL, Cable, etc.) without a quality of service option to give priority to the voice traffic, you will experience dropped calls and lower voice quality (something that recently happened to one of my customers).

So, which option is right for you? If you only need a few voice paths, not a lot of DIDs and have a reliable internet connection, then the SIP trunks are something worth considering. However, if you need something with a higher amount of voice paths and your business depends on reliable voice quality, the ISDN PRI is likely still your best option.