• A2P

    A2P, or Applicaiton-to-Person, messaging is one-way SMS to which recipients are not expected to reply. When you send a text message to vote for your favorite singer on the TV talent show, you are using A2P messaing. Software applications use an API to send an receive texts. 


  • Alphanumeric Sender ID

    Alphanumeric Sender ID allows you to set your company name or brand as the Sender ID when sending one-way SMS messages to supported countries. Alphanumeric Sender IDs may be up to 11 characters. Accepted characters include both upper- and lower-case ASCII letters, the digits 0 through 9, and space: A-Z, a-z, 0-9. They may not be only numbers.

  • API

    An Application Programming Interface (API) is provided by a service or program so that others may use the features and functions of the system. APIs are like a contract that describes how a consumer will make requests of the system, and what they will receive in return.

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  • C#

    C# (pronounced "see sharp") is a computer programming language created by Microsoft for use on the .NET platform. It is an object oriented programming (OOP) language and is statically typed. Its name comes from the C language, from which it inherits a similar syntax.

  • Call Tracking

    Call Tracking is a software-based performance marketing technique that generates and assigns a unique phone number to a specific advertisement or marketing campaign. Call Tracking systems then follow and analyze leads through that phone number “channel” to understand the channel’s true effectiveness and ROI or receive a commission for driving that lead.

  • Call whisper

    Call whisper, also commonly referred to as call screening, involves playing a message to the callee while the caller continues to hear ringing. It can provide additional information such as the source or purpose of the call to the callee before the call begins and even allow the callee to accept or reject the call based on that information.

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  • Direct Inward Dialing (DID)

    Direct Inward Dialing (DID) is a telephone service that allows a phone number to ring through directly to a specific phone at a business instead of going to a menu or a queue and needing to dial an extension. A phone number that is used like this is often called a "DID" (and multiple numbers are called "DIDs”).

    There are 2 ways to get DID-like functionality with Twilio Phone Numbers, via a SIP trunk, and with SIP registration. 

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  • E.164

    E.164 is the international telephone numbering plan that ensures each device on the PSTN has globally unique number. This is what allows phone calls and text messages can be correctly routed to individual phones in different countries. E.164 numbers are formatted [+] [country code] [subscriber number including area code] and can have a maximum of fifteen digits.

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  • GSM-7

    GSM-7 is a character encoding standard which packs the most commonly used letters and symbols in many languages into 7 bits each for usage on GSM networks.  As SMS messages are transmitted 140 8-bit octets at a time, GSM-7 encoded SMS messages can carry up to 160 characters.

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  • Interactive Voice Response (IVR)

    Interactive Voice Response (IVR) is an automated telephony system that interacts with human callers through the use of voice and touch-tone keypad selections (DTMF tones). It’s also commonly known as a phone tree.

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  • Long code

    A long code number is a standard phone number used to send and receive voice calls and SMS messages. Phone numbers are typically called “long codes” (10-digit numbers in many countries) when comparing them with SMS short codes (5-6 digit numbers).

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  • Masked Calling

    Masked calling is a technique used in ecommerce to protect buyers' and sellers' personal phone numbers private. It uses a short-lived phone number for each party, allowing them to communicate seamlessly during a specified time period. After the time period has expired, the numbers are recycled and reassigned to other parties on the platform, which helps keep transactions from happening outside the platform. 

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  • Network Address Translation (NAT)

    Network Address Translation (NAT) is the modification of in-transit network packets to map one IP address space to another.  It is most commonly used in IP Masquerading, where a large private IP network shares a relatively small number of publicly facing IP addresses behind a router or gateway.

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  • P2P

    P2P stands for Person-to-Person messaging. In simple terms, this is when two or more people communicate over text messaging. For example, when you send a text message from your phone to another person's phone, that's P2P. This can also include traffic that goes through an API to connect two people.

  • PSTN (Public Switched Telephone Network)

    The PSTN (Publicly Switched Telephone Network) is the network that carries your voice calls when you call from a landline or cell phone. It refers to the worldwide network of voice-carrying telephone infrastructure, including privately-owned and government-owned infrastrucure.

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    A REST API allows software programs to expose functionality and data to other programs over the Internet in a consistent format. APIs are considered RESTful if the means of accessing the API provider's functionality adhere to the architectural style of REST.

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  • SDK

    A software development kit, or SDK, is a downloadable software package that contains the tools you need to build on a platform.

  • Session Initiation Protocol (SIP)

    Session Initiation Protocol (SIP) is a signalling protocol for initiating, terminating, and modifying user sessions over an IP network.  Most commonly, SIP is used for Voice Over IP (VoIP) services, but is also often used for other communications sessions such as video calls and instant messaging sessions.

  • Short code

    A short code is a special 5 or 6 digit telephone number that's shorter than a full phone number. Short codes are used to send and receive SMS and MMS messages to and from mobile phones. Twilio currently offers short codes in the US, Canada, and the UK.

  • SMS Character Limit

    The character limit for a single SMS message is 160 characters, however most modern phones and networks support concatenation and will segment then rebuild messages up to 1600 characters.

    When you send a SMS message over 160 characters the message will be segmented into 153 character segements and sent individually then rebuilt by the recipients device. For example a 161 character message will be sent as two messages, one with 153 characters and the second with 8 characters.

    If you include non-GSM characters like eastern characters in SMS messages, those messages have to be sent via UCS-2 encoding. Messages containing any UCS-2 characters are limited to 67 characters and will be concatenated into 67 character message segments, even if the messages contain less than 160 characters.

  • SMS Gateway

    An SMS Gateway enables a computer to send and receive SMS text messages to a SMS capable device over the global telecomunications network, normally to a mobile phone. The SMS Gateway translates the message you send it and makes it compatible for delivery over the telco network to be able to reach the recipient.


  • SMS Message

    SMS stands for Short Message Service and is another name for text messages. SMS is the only standard to send text messages to almost any mobile phone, over the telecommunications network.

    A single SMS is limited to 160 characters however most modern mobile phones are capable of segmenting messages up to 1600 characters and re-assembling them on receipt. The limit was originally because SMS was designed to fit in between existing phone protocols and that limit was then enshrined in the SMPP Protocol, which is how text messages are transmitted between carriers.

    Natively SMS can't handle pictures, video or attachments so in 1999 the MMS standard was ratified. MMS stands for Multimedia Messaging Service and that enables people to send pictures, videos and attachments over text message.

    Once the multimedia is received by the destination carrier the carrier sends a SMS asking the phone to download the content.

  • SMS Tracker

    An SMS tracker is software that uncovers detailed information about the delivery and content of text and picture messages. It allows anyone to analyze an individual message or group of messages to see delivery patterns, encoding details, and error conditions.


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  • Twilio Markup Language (TwiML)

    TwiML, or the Twilio Markup Language, is an XML based language which instructs Twilio on how to handle various events such as incoming and outgoing calls, SMS messages and MMS messages.  When building a Twilio application you will use TwiML when communicating your desired actions to Twilio.

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  • UCS-2

    UCS-2 is an character encoding standard in which characters are represented by a fixed-length 16 bits (2 bytes).  It is used as a fallback on many GSM networks when a message cannot be encoded using GSM-7 or when a language requires more than 128 characters to be rendered.

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  • virtual phone number

    A virtual number is a standard telephone number that is not locked down to a specific phone. A virtual number can route a voice call or text message to any phone or workflow. In a simple example, a virtual number just forwards a call to another phone. With virtual numbers powered by an API complex software workflows can be built that are triggered by calls and texts.

  • Virtual SMS

    Virtual SMS enables you to send and recieve SMS text messages over the internet without having to use a physical phone. This is especially useful when you want to use software to communicate with telephone networks that would be impossible on a physical phone, e.g. Uber notifying a customer that their car is outside or to have local phone numbers in different countries.

  • Voice API

    A voice API is a tool for software developers to make and receive phone calls with a simple, easy to understand API. Behind the scenes, a voice API bridges the Public Switched Telephone Network (PSTN) and applications connected to the internet. By using a voice API, software developers can program voice calling into their applications without specialized telecommunications knowledge and hardware.

  • Voice Proxy

    Voice Proxy is also known as Masked Calling. It refers to the technique used to protect users' private information by providing an intermediary number so that neither party can see the other's true phone number for voice calls or SMS.

  • VoIP (Voice Over IP)

    Voice Over Internet Protocol (VoIP) is a category of hardware and software that enables voice calls to be made and received over the internet.

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  • Webhook

    Webhooks are user-defined HTTP callbacks. They are triggered by some event in a web application and can facilitate integrating different applications or third-party APIs, like Twilio.

  • WebRTC

    Web Real-Time Communication (WebRTC) is a collection of communications protocols and APIs originally developed by Google that enable real-time voice and video communication over peer-to-peer connections.

  • WebSockets

    A WebSocket is a persistent bi-directional communication channel between a client (e.g. a browser) and a backend service. In contrast with HTTP request/response connections, websockets can transport any number of protocols and provide server-to-client message delivery without polling.

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