Here are some common terms explained:

Broadband
A service or connection generally defined as being 'always on' (there is no need to 'dial up') and providing data speeds greater than 128 kilobits per second, thus making the transfer of data a lot quicker and the quality of sound and video, much higher.

Internet protocol (IP)
The method used for sending messages across the internet and similar networks.

Internet service provider (ISP)
A company that provides you with access to the internet.

Narrowband
A service or connection providing data speeds up to 128 kilobits per second.

SIP

<Simple answer>

SIP is the most popular Voice over IP (VoIP) standard. SIP enables people to have a second telephone line and number to make phone calls just like a standard phone, the only difference is you are using the Internet to carry the call.

<Technical answer>

The SIP protocol, an Internet Engineering Task Force (IETF) standard, is the most advanced VoIP protocol today. Among other things, SIP allows applications and devices created by multiple vendors to inter-operate with each other. SIP is used to establish, maintain and terminate multimedia sessions, including telephony, video, and other types of communication. A person only needs one SIP address to work with any SIP-enabled device they happen to be using at a particular moment. These devices may include cell phones, PDA's, computers, etc.

Unlike SIP's predecessors, which were modeled after traditional telephony protocols, SIP has been modeled after modern Internet data protocols and thus has the ability to scale with a distributed architecture. Since SIP is based on standard Web protocols like SMTP and HTTP, it is more intuitive for Web developers, and thus facilitates the creation of unique applications, such as 'find me/follow me' services. Deltathree chose to migrate its next generation network to SIP because of the protocol's superior attributes, including faster and more cost-effective application development, rapid service deployment, greater scalability, and lower hardware requirements.

Voice over Broadband (VoB)
VoIP services that allow you to make and receive calls over a broadband access connection - for example digital subscriber line (DSL) or cable.

Voice over Internet Protocol (VoIP)
A technology that allows you to make calls using internet protocol (IP), using either the public internet or private IP networks.