It's also possible to switch a call from a mobile device to a desktop line or vice versa. Business products generally offer several pricing levels based on the number of lines needed, ranging from approximately $20 per line for large organizations to $35 per line for smaller groups. Even from an administrative perspective, you should be careful, however, when migrating to a new phone system. Whether you're an individual just buying a new land line or a business moving from an old-style PBX system, or even just switching to a different VoIP provider, the process should be approached carefully and only after thorough planning.
The RTCP extended report VoIP metrics block specified by RFC 3611 is generated by an IP phone or gateway during a live call and contains information on packet loss rate, packet discard rate (because of jitter), packet loss/discard burst metrics (burst length/density, gap length/density), network delay, end system delay, signal/noise/echo level, mean opinion scores (MOS) and R factors and configuration information related to the jitter buffer. VoIP metrics reports are exchanged between IP endpoints on an occasional basis during a call, and an end of call message sent via SIP RTCP summary report or one of the other signaling protocol extensions. VoIP metrics reports are intended to support real-time feedback related to QoS problems, the exchange of information between the endpoints for improved call quality calculation and a variety of other applications.
Local number portability (LNP) and mobile number portability (MNP) also impact VoIP business. In November 2007, the Federal Communications Commission in the United States released an order extending number portability obligations to interconnected VoIP providers and carriers that support VoIP providers.[33] Number portability is a service that allows a subscriber to select a new telephone carrier without requiring a new number to be issued. Typically, it is the responsibility of the former carrier to "map" the old number to the undisclosed number assigned by the new carrier. This is achieved by maintaining a database of numbers. A dialed number is initially received by the original carrier and quickly rerouted to the new carrier. Multiple porting references must be maintained even if the subscriber returns to the original carrier. The FCC mandates carrier compliance with these consumer-protection stipulations.
^ White, C.M.; Teague, K.A.; Daniel, E.J. (November 7–10, 2004). Browse Conference Publications > Signals, Systems and Computer ... Help Working with Abstracts Packet loss concealment in a secure voice over IP environment (PDF). Signals, Systems and Computers, 2004. Conference Record of the Thirty-Eighth Asilomar Conference on. 1. pp. 415–419. CiteSeerX doi:10.1109/ACSSC.2004.1399165. ISBN 978-0-7803-8622-8.
That being said, Grasshopper doesn’t offer any conferencing tools. For that, you’ll have to sign up for—Grasshopper’s sister company. This service offers both video and audioconferencing, but it does cost an extra $10–$30 per month. That’s another strike against Grasshopper, since most providers in Grasshopper’s price range include conferencing features.
In the case of a private VoIP system, the primary telephony system itself is located within the private infrastructure of the end user organisation. Usually, the system will be deployed on-premises at a site within the direct control of the organisation. This can provide numerous benefits in terms of QoS control (see below), cost scalability, and ensuring privacy and security of communications traffic. However, the responsibility for ensuring that the VoIP system remains performant and resilient is predominantly vested in the end user organisation. This is not the case with a Hosted VoIP solution.
By default, network routers handle traffic on a first-come, first-served basis. Fixed delays cannot be controlled as they are caused by the physical distance the packets travel. They are especially problematic when satellite circuits are involved because of the long distance to a geostationary satellite and back; delays of 400–600 ms are typical. Latency can be minimized by marking voice packets as being delay-sensitive with QoS methods such as DiffServ.[16]
Phone Power is another home VoIP provider that runs its service using an on-premises device. This is called the Home Adapter and like other services, it sits between your phones and your Internet connection, though no other network is required. It can even function as a router on its own. While it's not the cheapest home VoIP solution we found, it's certainly well-regarded and mature with a wide variety of options and capabilities.
That's the basics of UCaaS, but the concept is constantly evolving to include more communication and collaboration technologies. Those capabilities also get tweaked to provide new benefits, sometimes general, sometimes aimed at specific business use cases, like call centers or help desk operations, for example. The key is integration. Voice is becoming integrated with other back-end apps.
While there are still a few other legacy protocols around, and a few non-SIP standards, such as H.232, SIP is what's used for the vast majority of modern VoIP phone systems. The most common use I've seen for H.232 has been in dedicated video conferencing systems. SIP, meanwhile, handles phone service, video conferencing, and several other tasks just fine, which is why its use is so widespread. Where it has trouble is with data security, but more on that in a bit.  

While it doesn't offer as many features as its business-class version, residential VoIP is still overwhelmingly attractive when compared to standard phone service; firstly because of its much lower overall price tag and second because it simply offers more features than an old fashioned long line. You can keep your current number, suffer zero restrictions when it comes to 911 or long-distance calling, drop your monthly price to a low fixed number, and take advantage of VoIP-only features like smart call routing, virtual numbers, and more.
Phone Power is another home VoIP provider that runs its service using an on-premises device. This is called the Home Adapter and like other services, it sits between your phones and your Internet connection, though no other network is required. It can even function as a router on its own. While it's not the cheapest home VoIP solution we found, it's certainly well-regarded and mature with a wide variety of options and capabilities.
Most businesses need a portable phone system that can be used anywhere. Of course, landlines do not meet this criterion, and no landline is suitable communication during the journey. The answer is a digital VoIP service that can be used anywhere in the world. All you need is an internet connection and your VoIP phone can be connected to any phone number in the world, whether it is connected to the VoIP network or not.
Unless you’re running a major business out of your house, chances are you won’t need or be interested in the ability to do video conferencing with dozens of people at the same time. The same goes for an auto attendant and business software integrations. First decide which features are priorities for you (unlimited calling, voicemail-to-email, international calling plans, etc.) and then take a look at what each company offers. After all, there’s no sense in paying for features that you don’t need. 
IP communication provides for device mobility. For example, a residential broadband connection may be used as a link to a virtual private network of a corporate entity, in which case the IP address being used for customer communications may belong to the enterprise, not being the IP address of the residential ISP. Such off-premises extensions may appear as part of an upstream IP PBX. On mobile devices, e.g., a 3G handset or USB wireless broadband adapter, the IP address has no relationship with any physical location known to the telephony service provider, since a mobile user could be anywhere in a region with network coverage, even roaming via another cellular company.
A critical part of the discussion with your IT staff will be whether your existing data network can handle the extra load that will be placed on it by the new phone system. You'll need a network that can handle more advanced network management capabilities, including tools to fight jitter and latency as well as to provide Quality of Service (QoS) and different kinds of network segmentation, especially virtual LANs (VLANs). Only tools like these can help free up your network from too much congestion, which can cause your call quality to decrease or even crash the VoIP system entirely.  
Throughout the developing world, particularly in countries where regulation is weak or captured by the dominant operator, restrictions on the use of VoIP are often imposed, including in Panama where VoIP is taxed, Guyana where VoIP is prohibited.[51] In Ethiopia, where the government is nationalising telecommunication service, it is a criminal offence to offer services using VoIP. The country has installed firewalls to prevent international calls being made using VoIP. These measures were taken after the popularity of VoIP reduced the income generated by the state owned telecommunication company.
Whether it's a dedicated bridge device or a special VoIP phone, you'll need something on the hardware side compatible with VoIP in order to access the technology's chief benefit: its software layer. It's at this layer where VoIP's advanced communication and collaboration features are enabled and how well the provider has leveraged those advantages will be directly reflected in how its proprietary hardware and back-end services are programmed. Whether it's a phone or a bridge, if you're worried about getting lost in technobabble when trying to setup your new phone service, remember that the best providers should be able to ship you pre-configured devices that shouldn't require much, if any, intervention on your part. With these, you simply plug them into your router or connect them to your Wi-Fi network and they'll go out and find the provider's network on their own. Just power them up, connect to your network, and wait for the light to turn green.

E911 (Enhanced 911) is a little different to traditional 911 services and is something that you should be aware of. With E911 you need to provide your home address, and this information gets passed to the emergency services if you dial 911. The concerns are that if you have a power outage or an Internet outage then you will not be able to dial 911. If you have a cell phone then you can dial 911 from your device. If you are ONLY reliant on VoIP for your phone service you should be aware of this situation.