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What to know before sending international SMS messages


Using the Short Message Service (SMS) across national boundaries has more considerations than getting a phone number.

People and organizations use Twilio to send SMS messages. Carriers consider all SMS messages from Twilio to be application-to-person (A2P), as your Twilio app sends messages to, and receives messages from, people. This behavior differs from person-to-person (P2P). Carriers consider P2P as communications between two or more people. To compare A2P to P2P, see the related Twilio Help article(link takes you to an external page).

Countries and carriers subject A2P traffic to different rules. Depending on the country to which you send SMS messages, you need to consider four factors:

  • What guidelines exist in the target country
  • How you want to identify yourself to recipients
  • What type of text you need to send
  • What type of other media you need to send

Target country guidelines

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Comply with national regulations on phone numbers

Make sure to comply with country regulations on phone numbers. Both Twilio and our customers must adhere to local country regulations. This often means you must provide adequate identity documentation to carriers or local regulators. Failure to do so creates a risk of disruption of service. Check the regulatory guidelines(link takes you to an external page) for phone numbers in the countries you want to target.

Recipients of your SMS messages might span the world. The guidelines you need to follow in sending SMS messages depend on where your recipients got their device. Twilio refers to the country in which recipients live as the target country. You must follow any A2P guidelines about SMS of the target country(link takes you to an external page). These guidelines might affect the timing, content, and permissions of your SMS messages.

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Examples


These guidelines also affect how senders identify themselves to recipients(link takes you to an external page). When only a physical device with an assigned phone number could send messages, the Sender ID was the same as the phone number. As senders cover a variety of devices and systems, the sender needs a Sender ID. Twilio refers to the country of the SMS sender as the origin country. A Sender ID takes three formats: a long code, a short code, or an alphanumeric ID. These formats vary in throughput capability, content type, and pricing.

Twilio offers the following Sender ID types:

Long codes

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These IDs send and display between 10 and 15 digits formatted per the International Telecommunication Union (ITU)(link takes you to an external page) E.164 standard.

These IDs send and display between three and seven digits depending on the origin country(link takes you to an external page).

These IDs present as a maximum of 11 alphanumeric characters.

  • Each target country can choose to accept this ID depending upon their regulations and 53 countries require ID registration.
  • Alphanumeric Sender IDs can include:
  • One hundred eighty-six countries support Alphanumeric Sender IDs.
  • WhatsApp doesn't support Alphanumeric Sender IDs.
  • Use Alphanumeric Sender IDs for low-volume, one-way messaging with branding.
  • If you use an Alphanumeric Sender ID with a Twilio Messaging Service, Twilio selects the Alphanumeric Sender ID when you send a message to a supported country.
  • These Sender IDs differ from a Caller ID Name (CNAM)(link takes you to an external page).
    • A CNAM determines what a recipients sees on their device in place of a long code.
    • An Alphanumeric Sender ID serves as the code itself. It isn't masking another number or code.

Summary of Sender ID features

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The following table outlines the support, throughput (in messages per second or Mps), registration requirements, timing, and general costs for the various Sender IDs.

Sender ID typeCountry supportMpsCountry registrationApplication timeCost
long code or 10DLCUS, Canada1Yes1 weekLow(link takes you to an external page)
toll-freeUS, Canada3No1 weekLow
long code190 countries(link takes you to an external page)10VariesVariesVaries
short code14 countries(link takes you to an external page)100Varies8-12 weeksHigh(link takes you to an external page)
alphanumeric186 countries(link takes you to an external page)10Yes, in 53 countriesUp to 16 daysVaries

To display and transmit text characters, a technology needs to translate text into data. Character encoding covers how something determines much data a text character needs and how the character gets translated. Some character encodings include only a few common characters while others provide as many as possible. The number of characters in an encoding is called a character set.

Twilio translates text characters into data using one of two standards: Global System for Mobile (GCM) communications and Universal Coded Character Set (UCS). GCM-7, the 7-bit character set for GCM, covers 128 of the common Latin-based characters. SMS, and Twilio, use GCM-7 as their default character encoding. UCS-2, the 16-bit character set, covers 65,535 characters including Chinese, Japanese, Korean, Hebrew, and Arabic characters among others. UCS-2 uses two bytes of data per character. When Twilio encounters a character not in the GCM-7 set, it changes the encoding of the entire message to UCS-2.

When SMS began, it limited messages to 140 bytes or 160 characters. To permit longer messages, SMS redefined messages as message segments(link takes you to an external page). SMS could split the message when sent and recombine it when received. To split and recombine long SMS messages, Twilio uses user data headers(link takes you to an external page). These headers take six bytes per message.

Character encoding matters because Twilio bills per message segment, not per message.

Encoding standardBits per characterCharacter set sizeCharacters per message segment
GSM-77128153
UCS-21665,53567

Only the US and Canada support Multimedia Messaging Service (MMS) messages. When sent to target countries that don't support MMS, the Twilio MMS Converter feature converts MMS to SMS. To turn off this feature, go to the Twilio Console SMS Settings(link takes you to an external page). To let your recipient access the media, these SMS messages include a link in the message body.


To start sending international SMS messages, figure out what type of message you want to send and to which audience. This use case helps you choose the best Twilio solution for sending global SMS.

  1. Review legal considerations.
  2. Review your target country support for long codes(link takes you to an external page), short codes(link takes you to an external page), and alphanumeric sender IDs.
  3. Review the support in your target countries for message concatenation, multimedia, two-way SMS, and UCS-2(link takes you to an external page).
  4. Apply for your long code(link takes you to an external page), short code(link takes you to an external page), or alphanumber sender ID(link takes you to an external page). This may include additional regulatory paperwork to complete outside of Twilio.
  1. Draft your SMS message.
  2. Review how Twilio encodes and segments your SMS message using this calculator(link takes you to an external page).
  3. Review the SMS pricing(link takes you to an external page) for the countries to which you plan to send messages.
  1. Review how to use Twilio Messaging Services.
  2. Review which mitigation features you need to send your message.