VoIP doesn't always completely eliminate the need for old-fashioned copper phone lines through the local telephone company. Sometimes the simple, cheap solution to supporting some devices is to keep them on the older technology.
Many businesses find it worthwhile to keep one or more copper lines in their communications systems mix because not everything that works well with the Public Switched Telephone Network (PTSN), also called “analog” and “copper” and often the simple solution is to keep those devices which are necessary to the business on analog connections running parallel to your VoIP system.
The reason is that over the years many auxiliary services have come to depend on the Public Switched Telephone Network (PSTN) and the way it works. These devices are tightly integrated into the PSTN and expect to be connected to the public switched network. Some of these services and devices have problems with VoIP and either work poorly or not at all with a VoIP system.
Fax machines are a classic example of a device that doesn't work well with VoIP. Although there are special gateways, fax machines, and servers for VoIP systems, conventional fax over VoIP is a chancy business.
Fax can be made to work if you adjust the settings on your fax device and don't try to send long faxes. (Four pages is normally considered the safe maximum.) However even then performance is generally spotty and there are a lot of retries.
The emergency telephones in elevators may require a special code to function, depending on the state you're in. These codes interfere with VoIP and the phones won't work over VoIP lines.
Burglar and fire alarm systems also have trouble with VoIP. The calling protocol is sufficiently different from PSTN that the alarm may not be able to contact the alarm central office via telephone. This renders the remote alert feature on most alarms useless.
This is becoming less of a problem as alarm companies adapt to VOIP systems. However this is still very much a hit or miss proposition.
Some alarm companies have versions of their systems that will work with VoIP. Some, on the other hand, won't support companies that use VoIP. Your alarm company should be able to advise you.
Credit Card Readers
The readers used to verify credit card use also have problems with VoIP. Most readers are build around analog modems that communicate between the merchant and the card company. These systems usually don't work over VoIP lines.
Some card companies offer readers that are VoIPcompatible. You need to check with your card company and see what they have available.
The first question is: Do you need these services? Most companies don't, which is demonstrated by the overwhelming growth in VoIP systems. Unless your business depends on one of these devices, such as fax, the simple solution is just to get rid of them when you go to VoIP.
Although there are work-arounds for many of these services, the simplest solution is often to keep one or more copper lines available for these devices. This is an additional expense, but in most cases it will be a comparatively small amount. Meanwhile you may want to explore options to allow you to discontinue the use of the services.
Many of these devices and services are supportable on VoIP systems by the use of special devices, such as gateways that will integrate them into the VOIP network. Often the choice between retaining one or more PSTN lines and adding additional equipment to your VoIP system comes down to economics. Is it cheaper to maintain some analog lines or to add the equipment to go to a completely VoIP system?