If you’re located in one of the 21 states currently serviced by Verizon Fios—which are mostly in the northeast—you’ll have access to one of the fastest internet connections available, which is perfect for VoIP. If you’re in DSL-only country, the speed will be slower, but uptime is still guaranteed at 99.95%. Either internet option will support steady VoIP service, and if your business is more medium-sized than small, Verizon could add up to a better value in the long run (especially if you’re in Fios territory).

While understanding the basics of VoIP and SIP is important, setting one of these systems up will require some general network knowledge, too. For the best quality, you will need to meet a minimum upstream and downstream data throughput requirement. In addition, you'll also need to meet a minimum latency number (that is, the time between when a signal leaves a remote computer and when your system receives it), typically measured in milliseconds. It is possible to test your network connection to see if it will support a VoIP service. RingCentral offers this service from their website, other vendors like to have their service engineers do it for you.  

A high speed Internet connection is required to "carry" your calls so if you have an Internet outage (or your ISP has an outage) then your phone service will not work. Internet services have improved significantly in the last few years and outages tend to be much less common than they use to be. Again, if you have a cell phone then this may not be an issue for you.
The interest that VoIP technology is generating for consumers and businesses alike, is creating a high level of demand that is being addressed by more and more providers entering the market. Choosing the best home phone service can now be a challenge as it can be difficult to compare providers that have different pricing structures, different features and different contract terms. Many residential providers names are becoming familiar in the home, such as Vonage, MagicJack and Ooma. Vonage, one of the more expensive options today, is popular due to its unlimited international calling feature. Evaluating Vonage competitors can save you even more money depending on your exact needs.
The most widely speech coding standards in VoIP are based on the linear predictive coding (LPC) and modified discrete cosine transform (MDCT) compression methods. Popular codecs include the MDCT-based AAC-LD (used in FaceTime), the LPC/MDCT-based Opus (used in WhatsApp), the LPC-based SILK (used in Skype), μ-law and A-law versions of G.711, G.722, and an open source voice codec known as iLBC, a codec that uses only 8 kbit/s each way called G.729.
On the higher end of this space, hosted PBX providers, such as RingCentral Office, will generally offer (sometimes even require) on-premises handset hardware, like desk or cordless VoIP phones that get sent to you pre-configured to work with their service. Plug the phones in, make sure they see an internet connection, and after some self-configuration time, your VoIP service goes live auto-magically.
Government and military organizations use various security measures to protect VoIP traffic, such as voice over secure IP (VoSIP), secure voice over IP (SVoIP), and secure voice over secure IP (SVoSIP).[39] The distinction lies in whether encryption is applied in the telephone endpoint or in the network.[40] Secure voice over secure IP may be implemented by encrypting the media with protocols such as SRTP and ZRTP. Secure voice over IP uses Type 1 encryption on a classified network, such as SIPRNet.[41][42][43][44] Public Secure VoIP is also available with free GNU software and in many popular commercial VoIP programs via libraries, such as ZRTP.[45]
The majority of plans are loaded with a great selection of features that can come in handy when you are making or receiving calls. Many providers offer over 30 features included in the low monthly fees. These include basic call management features such as call waiting, call forwarding, call blocking, caller ID name, do not disturb, and voicemail. More advanced features such as the voicemail to email feature let's you access your messages at anytime, even when you are away from your home, simply by checking your email inbox. Distinctive ringing, additional virtual numbers, and Smartphone Calling App's are other examples of more advanced features that can be useful.