Transitioning from a traditional PBX (or PABX) office phone system to a VoIP PBX can introduce a lot of difficult choices, from VoIP PBX system types to VoIP hardware to PBX vendors.

If you've already determined that an IP PBX is the best office phone system for your company, the next logical step is determining what the best IP PBX system is for your company.

IP PBX Advantages

If you've decided on an IP PBX system, you've made a good choice for your office phone system. IP PBX systems, complete with IP phones, have many advantages over a hosted VoIP PBX.

IP PBX phone systems offer many advanced business features, including hot desking functionality.

IP PBX office phone systems:

  • Are a true converged system, using one network for voice and data
  • Eliminate the need for phone wiring (IP phones connect to the Ethernet)
  • Enable the use of softphones and video phones
  • Are on-premises
  • Can use the company's LAN for internal calls
  • Support VoWiFi phones
  • Don't need SIP trunks
  • Support hot-desking (configuration travels with phone)
  • Save money on long-distance and international calls
  • Support video IP phones

Additionally, with an IP PBX office phone system, businesses don't have to pay a per-seat monthly fee as they would with a hosted PBX.

How to Choose the Best IP PBX


Of all the factors involved in this decision, this one floats to the top of the list for obvious reasons. What kind of IP PBX system can you afford? What's your budget? How many people do you need to accommodate? What features do you need/want?

IP PBX phone systems are a wise choice for small or midsized businesses, especially those with expansion plans in their future. A VoIP IP PBX system is designed for businesses with 20 or more employees, and like a hosted PBX can easily accommodate branches and remote employees. As a business telephone system, an IP PBX can grow with an organization, making it easy to add new locations as well as extensions.

An IP PBX can be somewhat more expensive than a hosted VoIP initially, and the real economic benefits are seen over time (and lower phone bills). IP PBX systems can range from under $1,000 for small businesses (the 4-line Grandstream GXE5024 with legacy PSTN trunks checks in at $555 on to over $5,000.

The open-source, Asterisk-based Sigma IP PBX Sig 320 for mid-sized businesses can accommodate up to 200 users, and is priced at $2,395 on (2/24/12). The Digium Switchbox AA355 appliance (software and warranty extra) supports up to 400 IP telephones/users, and is available at for $5,950 (2/27/12). A Talk-A-Phone PBX-64 retails for $8,599.95 at (2/24/12).

IP Phones for IP PBX Systems

Similarly, IP phones (or IP HD phones) are more expensive than traditional phone hardware. An entry-level Grandstream GXP 1400 HD IP phone with just two lines retails for $55 on (2/24/12), but a Polycom SoundPoint 650 with Polycom HD Voice that supports 6 lines sells for $252 on (2/24/12). Nortel's 6-line 1140E (not an HD phone) lists for $295.00 (Amazon, 2/24/12).

IP PBX systems, because they are transmitting everything as data, can also support IP video phones. Video phones are even more costly than voice-only IP phones, and can range from under $150 for a low-end model to over $1,000. offers 8 entry-level Grandstream GXV3000 IP video phones for $1,699.97. A Cisco Unified IP Phone 8941 with Power over Ethernet (PoE) is $299 on (2/27/12). The Polycom VVX 1500 retails for $749 on (2/27/12).

If you are going to invest in video phones, you need to make sure the codecs and protocols are supported by your IP PBX system. Standard video codecs are H.263 and H.264, and the open-source SIP protocol is the most flexible.

Compatibility and Integration

Even though you're replacing your current PBX, which is most likely a PABX in dire need of an upgrade, you should consider the crossover period. Can the two systems 'talk' with one another? Should they?

The short answer is yes. To ensure a smooth transition and continuity of service, the best IP PBX phone system is one that integrates with your current PBX phone system. Otherwise, you'll be without phone service while you switch your current PABX off and get your new IP PBX system set up.

On the other hand, if the two PBX systems are both on and working together, migrating everything over from one system to the other will be relatively simple. Compatibility will ensure there are no bumps in the road.

You should also look for an IP PBX that offers the most flexibility. The best IP PBX integrates with a variety of IP phones (vendor independence), Exchange and other Microsoft products such as OCS (Office Communications Server), and other computer telephony integration (CTI) devices, interfaces, and applications. For failsafe consideration, choose an IP PBX that also offers integration with PSTN gateways.

Before you do anything, of course, you need to be sure that your network can support an IP PBX as currently designed. VoIP calls require more bandwidth and can tax a poorly structured network, dragging down the system altogether. First the voice calls will become unreliable, and then as they disrupt the network, all data transfers will be affected (email, etc.).


An IP PBX is a completely digital office phone system, offering true convergence of voice and data over the Internet. An IP PBX offers a lot of advantages over a traditional PBX, or even a hosted VoIP PBX, but choosing an IP PBX also means that you need to plan well. If your Internet goes down, so does your phone. If there's a power outage, you need to have a backup alternative for outside access. The best IP PBX phone system incorporates fail safes for power and network loss, such as PSTN interfaces.

The best IP PBX is one that consistently gets solid reviews by users. Check forums and blogs online, or comments posted on trade articles, for recommendations and performance assessments by people who are already using the IP PBX system you have in mind.

Another way to find the best IP PBX is to consider an IP PBX system with features that mitigate failures and outages. Look for features such as:

  • Automatic server failover
  • Disk redundancy
  • Power supply redundancy
  • Redundant trunks
  • Monitoring and report features
  • Guaranteed 99% uptime
  • Remote access
  • Load-balancing mechanisms/overload control
  • Automated alerts
  • Designated extensions connected to outside lines (always)

You may also want to consider a redundant ADSL/SDSL line, uninterrupted power supplies (UPS), and a generator.

When investing in a business telephone system, the best IP PBX phone system is usually one that is open source or vendor-independent. For true reliability and cost-savings, an operating system that is not tied to one manufacturer offers more flexibility and growth potential. PBX vendors that lock you in to a specific or proprietary software solution may also impact the speed of expansion or repairs as well as the cost.

Open-source software also allows for customization, which is why many businesses choose a Linux-based OS. However, if the company's network is not Linux-based, it may be easier to stick with an IP PBX that uses Windows.

Advanced Call Controls

When choosing an IP PBX phone system, don't forgo any of the convenience features you would get with a hosted VoIP PBX. The best IP PBX should have all the advanced telephony features of VoIP office phone systems. In fact, the better IP PBX systems will have the call control features a hosted PBX would consider as extra or optional included as standard features.

The best IP PBX should have features such as:

  • Voicemail-to-email
  • Conference calling
  • DID and extension dialing
  • Cell phone integration
  • Multiple phones per extension (including remote phones)
  • Call park

Support and Training

The best IP PBX office phone system offers options for round-the-clock support and ongoing training. In most cases, support is a feature of your IP PBX that will go unneeded and unused — the best scenario — but in the event of any sort of failure or problem, you need to be sure that a support line is manned 24/7.

Before committing to an IP PBX system, be sure you know the cost parameters as well. Does your PBX vendor charge per incident? Does it offer a yearly, flat-fee contract? Are there additional charges for after-hours or holiday incidents?

How well-trained are the technicians providing phone support? Do they have certifications? A good reputation? Do they explain things simply? Are they understandable? The best IP PBX phone system will offer clear, efficient, and economical support.

If you've opted for an IP PBX, then you have decided that an on-premises PBX is the best solution for your company and that your IT staff is proficient enough to handle the challenge. However, that doesn't mean the IT department will know how to manage the IP PBX automatically. They need to be given the proper training — and ideally that should be provided by PBX vendors. Additionally, training may also have to be factored into your IP PBX budget.