The low cost of VoIP is its biggest attraction. Business VoIP services are significantly less expensive than traditional phone services. You have much less hardware to buy or lease; in fact, many hosted services require no new hardware investment at all. If you do need hardware, it's typically based on standardized technologies such as SIP, as opposed to proprietary products that tie you to a particular service provider. Monthly subscription fees are lower, as well. Verizon Small Business plans with unlimited nationwide calling, for example, start at just $63.50 per line, while Vocalocity offers the same unlimited calling with even more features for $40 per line. VoIP services also tend to be contract-free.
VoIP is cheaper than a traditional landline if you have staff in far-flung locations. Since in-network calls travel exclusively over data networks and don't need to hit the public phone lines, most VoIP providers let you make calls to your coworkers for free, even if you're in New York and they're in San Francisco. Don't worry, do-it-yourselfers: IP-PBX servers can handle remote employees as well.
Many hosted VoIP providers offer mobile apps that let you make and receive calls from the road using your data connection. Usually you can adjust the apps to ring simultaneously with your office phone or to act as a stand-alone extension.
Scalability is another boon. Rather than having to invest in costly new hardware, adding new extensions to a VoIP network is typically as easy as connecting your SIP-enabled phone to the network and tinkering with some software settings--and if you use a phone that's certified for use with your provider or software, it could be as simple as plug and play.
Most VoIP providers and IP-PBX software packages deliver a much more robust feature set than traditional phone providers do. All the basics you'd expect are present--including conference calling, voicemail, Internet faxing, and caller ID--but VoIP services also often supply virtual receptionists and greeting functionality, customizable advanced call screening and forwarding rules, integration with office software, and the ability to forward voicemail to your email or your mobile phone. Many providers offer these advanced features as part of a subscription; even when you must pay extra, the cost is usually less than you would pay a traditional phone provider for the same services.