Very simple one and two line phones or key telephone systems with 4 to 6 outside lines are set up for analog phone lines. The simple VoIP services use an analog phone adapter to connect to DSL broadband service to provide 1 or 2 lines. That's pretty much the extent of what you can do with these simple systems. Once you get more than a half-dozen outside phone lines, you should be looking at T-1 service as a cost saver.
There are several flavors of T-1 line services to be aware of. A standard T-1 telephone trunk offers up to 24 individual phone lines all digitized and multiplexed into two pair of copper wires that connect back to the telco central office. Your PBX system needs a T-1 interface card to connect to a T-1 line. These are pretty much a standard option for any new PBX phone system and you can likely order a plug-in T-1 card for older systems.
A variation on the T-1 line is called an ISDN PRI or T-1 PRI phone line. PRI stands for Primary Rate Interface and it's part of the ISDN or Integrated Services Digital Network specifications. A regular channelized T-1 line and a T-1 PRI line are pretty much the same animal, with one important difference. PRI lines offer 23 rather than 24 phone lines and use the remaining channel to provide signaling and data. You need a PRI line if you want Caller ID for your phones.
Another variation is called T-1 Integrated service. Integrated means that the line carries both telephone calls and Internet data. That's right, you can split a T-1 line so that you can have a dozen outside phone lines plus broadband Internet service coming in on the same line. This is quite a cost saver for most small businesses that need both phone and reliable Internet service. Some of these Integrated services are called dynamic T-1 lines because they automatically assign all the bandwidth not needed for active phone calls to the Internet service.
What about VoIP phone systems? Most Enterprise VoIP phone systems use IP telephony within the company so that the phones can connect to the IP PBX system using standard Ethernet cabling. Many use the same LAN as the company's computers to save on wiring costs. All the in-house calls go from phone to phone over the network. But outside calls still have to connect or terminate to the PSTN or Public Switched Telephone Network. Most often that interface is within the IP PBX system or voice gateway. The most common phone line interface is the T-1 or T-1 PRI digital phone line, just like conventional PBX systems.
Another option that's not quite as widely deployed is to connect your phones to a VoIP service provider in IP format directly from your network. The service provider takes care of terminating calls to the PSTN. The network connection from your company to the service provider is called a SIP Trunk and is most often a type of T-1 line set up to be unchannelized to transport voice packets.
You should know that T-1 line prices are lower now than they've ever been. If you're still using analog phone lines connected to your PBX telephone system, it may well be worth your while to convert to one or more T-1 or T-1 PRI lines. If you already have T-1 service, then you should get a competitive quote to see how much you might save on your next contract. Simply enter a quick online quote request at T1 Rex.
