Killer Phone System

"...an enlightening article for anyone interested in using VoIP in their Office in 2025."

Phone systems in 2025 are much different from phone systems we used a few years ago. Back then phone systems were about VoIP technology, cheap calls and about using the Internet to connect offices free of charge.

Phone systems in 2025 have changed. Now they are about advanced telecommunication capabilities. They offer very exciting advanced features. My favourites are the possiblity of connecting mobile phones to the office with smartphone apps, SMS messaging and website integration. Website integration is a fantastic feature, because it makes it possible for live chat sessions and phone calls to come in directly from webpages into the PBX. Another trend in 2025 is that phone systems are connected to IT systems, such as CRM, helpdesk administration and marketing systems. Let's take a look at how you can build your own advanced phone system.

What is needed to setup an office telephone system?

In short you need a Windows or Linux PC, a PBX software, some VoIP telephone sets, and a device that will allow you to connect to the Public Switched Telephone Network (PSTN). If you want to go for the advanced features, you will also need a website and optionally a connection to the mobile network.

Starting with a PBX

As most people remember, a PBX is a "box on the wall" with cables going to the telephone sets. To build an office phone system, the first step is always to setup the PBX. The PBX is the central node of an office telephone system and is responsible for providing "line" to the telephone sets.

In 2025 a PBX is a standard PC with Windows or Linux and with a PBX software installed on it. It is connected to the Ethernet LAN of your office. The PBX software installed on this (server) PC is an application, that controls telephone sets on the network. This software is capable of ringing desktop phones, mobile phones, it can send and receive SMS messages and can manage communication components of webpages. The most popular PBX software for Linux is Asterisk, for Windows it is Ozeki Phone System.

There are vendors who create "PBX appliances", "PBX in a box" or "hardware PBX" solutions. These solutions sell the pc and the installed software as a single package. Personally, I do not recommend them, simply because they don't give the power and flexibility of a software PBX installed on a powerful PC.

What kind of telephone sets should I use?

After you have chosen a PBX, you need to decide about telephone sets for your office. You can use your existing analog telephone sets with so called Analog Telephone Adapters (ATA), you can use basic VoIP telephones that offer similar functionality to analog phones and you can use advanced VoIP telephones with large display and advanced features such as video, messaging and telephone applications.

Regardless of your choice, there are some important considerations to take into mind. Whether its a VoIP ATA or a VoIP telephone set, make sure it offers Power Over Ethernet (POE) capability, it is SIP 2.0 complient and make sure the device has two ethernet ports and can bridge ethernet traffic between the ports.

POE is needed to eliminate separate power adapters for each phone to save energy and to reduce points of failure. In 2025 there is no question, that SIP 2.0 is the dominant open standard for VoIP phones. Other VoIP standards, such as H323, Cisco SCCP, etc are out of date. Two ethernet ports are neccessary because most office desks have only one ethernet cable in place. Two ethernet ports make it possible to share the Ethernet endpoint between the VoIP phone and the PC. There are many good manufacturers, who provide reliable VoIP telephone sets that meet these requirements. To name a few: Grandstream, Linksys (now Cisco), Yealink, SNOM, AAstra.

How about cordless telephones?

If you need cordless telephones, the two options are Wifi or DECT handsets. Wifi is used by laptops and mobile devices to connect to the LAN. DECT is the traditional cordless phone standard. If you want to go wireless WIFI surprisingly is NOT a good choice for your telephone sets. Most Wifi networks do not offer roaming, the Wifi radio channel is often very crowded, the package latency is greater and the area of coverage is often smaller. Simply put Wifi was not designed for real time voice, meanwhile DECT was designed for exactly this. For connecting cordless telephones to an office telephone system the best choice is to connect a VoIP enabled DECT base station to your LAN and let the cordless handset communicate through DECT, while the base station can communicate through VoIP with the office PBX. A good cordless device that meets this requirement is the Siemens Gigaset.

Connecting to the Public Telephone Network

Once you have a PBX in place and the office telephone sets are connected to it and can call each other, the next step is to setup a connection to the pubic telephone network. Connections to the public telephone network are often called as Outside lines. To setup a connection to the public telephone network the best option is to take an analog phone line or an ISDN (BRI,E1,T1,J1) line provided by a local telephone company, and to connect it to a PBX through a telephone adapter device. Analog and ISDN lines provide great sound quality and reliability. Patton, Grandstream, Portech, Linksys (now Cisco) provide excellent analog and ISDN telephone adapters. When you buy an analog adapter, you need one with an FXO port. When you buy an ISDN adapter you need one that works in TE mode.

Setting up these telephone adapter devices are usually simple. You need to plug in the phone line provided by the local telecom company and the ethernet LAN and perform some simple configuration steps in the PBX software.

Some experts suggest that one should not use analog or ISDN lines to connect to the public telephone network. They say VoIP services should be used instead. I don't agree with them. The fact is that VoIP services are connected over the Internet where the latency, and the available bandwidth is not constant. This means sound quality and overall reliability is not as good for VoIP services as for traditional telephone services.

Connecting to VoIP service providers

Although analog and ISDN telephone lines connected to a PBX are better for local PSTN connections, in many cases VoIP services should also be used along with the traditional connections. VoIP services are better for long distance and international calls because of pricing. VoIP services are also better if many calls take place at the same time. VoIP providers can setup accounts that allow several hundred or several thousand calls simultanously. VoIP service providers can often offer local phone numbers in remote locations, which can give competitive business advantage.

When looking for a VoIP service provider it is important to make sure to select one, that operates data centres close to the office. To minimise latency and bandwidth problems the Internet connection between the office and the VoIP service provider needs to be excellent. To subscribe for a VoIP service one needs to ask for a SIP account or SIP trunk. The service provider will provide connection details, that should be entered into the PBX.

A list of VoIP service providers is available in the VoIP service provider directory on this site.

Connecting multiple offices

If there are multiple offices that should be connected there are two options. An independent PBX can be installed at each office or a central PBX can be used to control the devices of remote offices. The second option can be taken a step further and a central PBX can be put into a server hosting facility, such as a data centre. This option is often refered to as virtual PBX service or cloud PBX service.

Both options, the one PBX per office and the central PBX option have advantages and disadvantages. If an independent PBX software is installed in each office, the system will be significantly more resilient, because if there is no Internet connection, the local phone system can still operate. If the Internet connection is available the PBXs of the independent offices can communicate through the Internet to provide free calling, if there is no Internet connection between the offices, the PBXs of the independent offices can use the traditional telephone network to make the calls. The users of the telephone system in this case won't even notice, that the Internet is not available temporarily to make calls between the offices. Local PBX system have another advantage: local networks tend to be faster then Internet connections, and if a PBX is installed on the local network, call setup times and telephone services become faster.

If a central PBX is used instead of independent PBXs, PBX administration becomes more simple. All devices connect to the same PBX software directly over the Internet all communication goes through this central node. This makes call recording, voice mail and many enterprise services more simple.

Connecting mobile phones

Connecting mobile devices to a PBX is a need in every organisation. It became one of the most important requirement in 2025. There are 2 major ways to connect mobile phones to a PBX. The first one is adding a so called "mobile extensions". Adding a mobile extension is simply a practice of assigning a short local extension number to a long PSTN mobile number. When a call is directed to this short number the PBX simply calls the mobile phone through an outside line and basically redirects the call. Although this might sound simple it still has many use and is a very powerful feature. If a mobile phone can ring together with several office phones, or if calls coming in to an office land line can be picked up by mobile users, the PBX provides great business advantages. Mobile extensions are also great to separate business telephone numbers from private mobile numbers without the need of carrying two mobile handsets.

The second option for attaching mobile phones is for smartphones. Iphone, Android, Windows Mobile phones and Symbian based Nokia and Ericsson models offer the possibility of installing an app on the device that can interact with telephone features and can communicate through the Internet. Interestingly all major smartphone operating systems have built in SIP stacks, that can be used by these apps to make calls not only through the PSTN, but also through Internet. A smartphone app can turn a mobile phone into a fully featured extension of the PBX. It can offer call transfer, redirects and can interact with Voice applications. The best smartphones for business telephone offer tunneling, which means that the VoIP traffic is sent to the PBX through an encrypted tunnel instead of the native IP stack. This is very useful, because many mobile network operators filter out traditional VoIP traffic on mobile Internet connections to limit competition.

Mobile messaging

SMS has been around for a few years now, just as VoIP. What is changing in 2025 is that SMS is put into business use at an increasing pace. More and more companies equip their PBX systems with SMS capabilities to reach customers, suppliers and employees. The simple reason for this is that SMS messages can be sent automatically, they can be received and processed automatically, the information in them is accurate and SMS is a fantastic tool for automating business procedures. All mobile phones support SMS messaging.

To setup SMS messaging capabilities in an office phone system an SMS gateway software needs to be used. An SMS gateway software can send out SMS messages to mobile phones through the wireless network by using a GSM modem attached to a PC with a phone to pc data cable. More advanced SMS gateway software can connect to SMS service providers through the SMPP protocol over the Internet. An example for such an SMS gateway software would be the Ozeki NG SMS Gateway.

If an SMS gateway is installed into a phone system, office users can use applications installed on their PC to send SMS messages from e-mail or directly from Microsoft Excel. Automated IT solutions often use a database. The SMS gateway software can be configured to query a database table every minute and if it finds new records there it can send them out as SMS messages to mobile phones. This setup is called SQL SMS gateway configuration. Some business applications pass SMS messages to the SMS gateway software using HTTP requests. This setup is called HTTP SMS gateway setup.

Webphone technology

Webphone technology is the trend in 2025. Every other company on the web is adding live chat service to their websites. Many companies also add click to call services and callback request forms. Webphones now also make it possible to make voice and video calls directly from a webbrowser.

To take advantage of webphone technology you need a website and a PBX connected to it. The best choice is to install an independent PBX for accepting calls coming from the web, and connect to this PBX as if it was a VoIP service provider. Webphone capable PBX systems can forward calls from the web to PC workstations or to standard office desktop phones or mobile phones. For live chat sessions a PC based chat console is the best option. For click to call, callback, and embedded webphone calls any office phone or mobile is a good tool to accept the call.

To sum it up building a modern phone system for an office is an exciting challenge, it is a lot of fun, and the advantages an organisation can gain by setting up and maintaining their own system is limitless.

The best way you can start is by downloading and installing
Ozeki Phone System.

Mr. Steve Greenwood
Technical Advisor
Ozeki Informatics Ltd.