Much easier to install & configure than a proprietary business phone system:
IP phone systems run as software on a computer and can leverage the advanced processing power of the computer and user interface as well as features. Anyone proficient in networking and computers can install and maintain an business IP PBX. By contrast proprietary systems often requires an installer trained on that particular business system!

Easier to manage because of web/GUI based configuration interface:
An IP PBX can be managed via a web-based configuration interface or a GUI, allowing you to easily maintain and fine tune your business VoIP solution. Proprietary phone systems have difficult-to-use interfaces which are often designed to be used only by technicians.

Significant cost savings for your business using VoIP providers:
With an IP PBX you can easily use a business VoIP Provider for long distance and international calls. The monthly savings are significant. If you have branch offices, you can easily connect between branches and make free calls.

Scalable:
Proprietary solutions are easy to outgrow. Adding more business lines or extensions often requires expensive hardware modules. In some cases you need an entirely new business system. Not so with an IP PBX. A standard computer can easily handle a large number of lines and extensions – just add more telephones to your business network to expand!

Twice the telephone system features for half the price!
Since an IP PBX is software-based, it is easier for developers to add and improve feature sets. Most VoIP  business solutions come with a rich feature set, including auto attendant, voice mail, ring groups, and advanced reporting. Unified Communications features are included, to support presence, video and audio conferences and free calls via the data network. These options are often very expensive in proprietary business solutions.