Telephone, Mobile, and SMS Abridged Glossary


Technical texts and technical people tend to use a lot of acronyms for concepts, and more than often they assume that these are widely known and understood by their audience, which is not always the case.

If you dealt with savvy customers, geek employees, or perhaps took support from your telephone or SMS provider, it’s highly probable that some of these words came up at some point in a call or chat. If you didn’t know the meaning at that time, don’t despair, that won’t happen to you again, we promise 🙂

We’ve put focus on choosing the most common words used when discussing telephony, mobile, and SMS topics for your delight and learning, mostly taken from the “Concepts” section of our FAQ, where you will be able to dig into the gory details of each term if you need to.


P2P (Person To Person) and A2P (Application To Person)

These words are used when talking to how a message service is used. P2P states that messages flow between humans, while A2P means that messages flow between a human and an application, usually providing services for their users (e.g: home banking, 2 factor authentication, notifications and alerts, etc).

You can read more about A2P in our blog posts “SMS A2P is on! Are you?” and “How To Create An Amazing Customer Service With SMS“.

CNAM (Caller ID Name)

Carriers share a per-country database where they have associated each country phone number with a name, this is called the “Caller ID Name” (e.g: you can make your own name appear in caller ID devices when calling from your phone number).

This database can be queried for your own purposes (for example, to enhance your leads when receiving calls or before calling a customer, so you get their name in advance). You can read more in our blog post “Improving Leads Quality with Caller ID Information

DID (Direct Inward Dial), or Long Code, or LVN (Long Virtual Number)

A DID or Long Code is just a phone number in E164 Format (this is a fancy term to say that country and area code are included in the number, see below for the description of the E164 meaning).

Anyone in the world should be able to make a call to a DID. An example is our toll free number: +18447839863. For more information head to the DID Section of our FAQ.

SC (Short Code)

A short code is different from a DID. They are country specific (you can only send and receive messages to/from a short code if you have a mobile service from that specific country) and they are mostly used for marketing campaigns (e.g: text DEALS to 12345 for the best deals!).

Read more about Short Codes and their use in our FAQ Section for SMS Services.

MT (Mobile Terminated)

This means that a given text message ends in a mobile device (meaning outbound messages from your PortaText account). See also What is “MT” or “Mobile Terminated”?

MO (Mobile Originated)

This term describes messages sent from a mobile device (inbound messages to your PortaText account). See also What is “MO” or “Mobile Originated”?.

GSM (Global System for Mobile Communications)

GSM is a standard that describes what’s behind the 2G cellular networks used in mobile communications. 3G and 4G are not part of it. You can read more about GSM in What is “GSM” or “Global System for Mobile Communications”?.

GSM 03.38 (GSM Charset)

The GSM 03.38 Recommendation is the character set allowed in the GSM standard to send and receive text messages. Depending on the encoding used, your messages will be limited to 160 or 70 characters. You can also read more in our blog post “Unicode in your SMS: Emojis and Non-English Characters“.

Here you can find the complete GSM 03.38 character set.

MNO (Mobile Network Operator)

An organization in control of a radio spectrum and with all the needed equipment and services to offer and provide mobile services to end users. It may also sell its services to a Mobile Virtual Network Operator (see below). For more information see our FAQ Entry about MNOs.

MVNO (Mobile Virtual Network Operator)

An organization that offers mobile services to end users but without its own network. It will buy services from an MNO instead and resell them. For more information see our FAQ Entry about MVNOs.

ITU (International Telecommunication Union)

The International Telecommunication Union creates standards for devices and protocols for data, voice, TV broadcasting, next-generation networks and many other fields. For more information see What is “ITU” or “International Telecommunication Union”? What is the “ITU-T”?

ITU-T (Telecommunication Standardization Sector of the ITU-T)

ITU-T is the Telecommunication Standardization Sector of the ITU, that creates the ITU-T Recommendations. For more information see What is “ITU” or “International Telecommunication Union”? What is the “ITU-T”?


E.164 is an ITU-T Recommendation stating how to write any telephone in the world: limiting the number to a maximum of 15 digits including international country code, area code, and local number. To know more, see our FAQ entry about E.164.

PSTN (Public Switched Telephone Network)

The global network composed of all the national, regional, and local networks of the world, allowing any phone to reach any other phone in the world by making a telephone call. Read more in our FAQ entry for PSTN.

PLMN (Public Land Mobile Network)

A network owned and operated by an MNO for providing mobile telecommunications to the public. Each network is identified by its MCC and MNC (see below) and needs to be connected to the PSTN to reach other telephone numbers in the world. To know more read our FAQ entry for PLMN.

HLR (Home Location Register)

An architectural component of a GSM network. It’s a database that contains all the numbers and service information for all the subscribers that are allowed to use a mobile network. Read more in our FAQ entry for HLR.

MSISDN (Mobile Station International Subscriber Directory Number)

The telephone number to the SIM card in a mobile phone. A SIM has a unique IMSI (see below) that does not change, while the MSISDN can change in time. See our FAQ entry for MSISDN.

IMSI (International Mobile Subscriber Identity)

A unique (worldwide) number that identifies a user of a mobile network, also used to query the HLR for service details. This number is provisioned in the SIM card. Read more in our FAQ entry for IMSI.

MCC (Mobile Country Code) and MNC (Mobile Network Code)

The pair of MCC and MNC uniquely identify an MNO in the world. And, along with the MIN, they form the IMSI (see below). Read more in our FAQ entry for MCC and MNC.

MIN (Mobile Identification Number)

A unique number that an MNO uses to identify a mobile phone. It’s also the last part of the IMSI. Read more in our FAQ entry for MIN.

SIM Card (Subscriber Identity Module)

A hardware device (a chip) that holds the IMSI and it’s used to identify and authorize a mobile device to use a mobile network. Read more in our FAQ entry for SIM.

DLR (Delivery Receipt)

A status notification for the delivery of the message. This usually indicates if the message was accepted by the final mobile network or not. Read more in our FAQ entry for DLR.

SMPP (Short Message Peer-to-Peer)

SMPP is the protocol used to exchange SMS messages between Short Message Service Centers (SMSC) and/or External Short Messaging Entities (ESME). Read more in our FAQ entry for SMPP.

PDU (Protocol Data Unit)

When talking about SMS, a PDU often means a “Protocol Data Unit” of the SMPP protocol. A PDU is the minimum unit of data exchanged between peer entities (in the same layer) of a network. Read more in our FAQ entry for PDU.

SMSC (Short Message Service Center)

In the SMPP protocol, a Short Message Service Center (or SMSC) is a network element in the mobile telephone network. It stores, forwards, converts and delivers SMS messages. Read more in our FAQ entry for SMSC.

ESME (External Short Messaging Entity)

In the SMPP protocol, an External Short Messaging Entity (or ESME) is an external application that connects to a Short Message Service Center (SMSC) to engage in the sending and/or receiving of SMS messages. Read more in our FAQ entry for ESME.

— The PortaText Team.