Local Numbers and International SMS

June 24, 2019
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Twilio SMS Best Practices Part 3: Local Numbers and International SMS

International SMS is tricky. Global telecommunications regulations vary from country to country and are always changing. Twilio follows regulations diligently so we can protect our customers from getting penalized. At the same time, we want to make things easy. This blog will guide you through the best practices and nuances of using different types of phone numbers in different countries. It will also cover sender IDs, another way to send your SMS messages!

Number Types

Number types are different in each Country. Here in the United States we have:

Long code

A standard 10 digit phone number. There are two different types of long code numbers:

  • Local number
  • Toll-Free number

In other countries, you might see “long code” equivalent numbers, such as

  • Mobile numbers
  • National numbers
  • Multi-Function numbers

These number types may have different meanings in each country where they exist. Also, they are not always 10 digits long.

Short code

A special 5 or 6 digit number. These numbers are pre-approved by carriers and allow high throughput. That means they’re great for sending high-volume and/or time-sensitive messages. However not all countries offer SMS messaging through short code numbers. In addition to this, Twilio does not currently support every country that does, but we’re working on it!

The most important thing to remember as you start to scale into International markets is to identify each country’s unique number types and choose the number type that’s right for your use case….. Or…… use a Sender ID!

Sender IDs

Sender IDs, otherwise referred to as “Alphanumeric Sender ID”, “Dynamic Sender ID” or just “Alpha”, allow you to send messages using alphanumeric characters, usually a personalized sender name (instead of using a Twilio phone number).

You don’t need a phone number to send a message using a Sender ID. When you’re making your API Request, rather than using an E.164 formatted Twilio Phone number for the "From" value, you can use a custom text string like your company's name, as shown below: 


Sender IDs are supported in two different ways:

  1. Pre-registered Alphanumeric - Laws mandate that you must register your alphanumeric sender ID with local authorities in some countries. Furthermore, many of these laws specify that your messages cannot contain content that is considered to be advertising, marketing or solicitation. Twilio can help you through the registration process, which will often involve validating proof of company registration and messaging use case..
  2. Non Pre-registered Alphanumeric (or just “Alphanumeric”, or just “Twilio supports it and it does not require carrier registration”) - Not every country requires that you register your alphanumeric sender ID and still supports sending messages from an alpha ID. However, some of these countries do have guidelines on message length. At Twilio, we just call this “Alphanumeric Sender ID”.

The easiest way to find out which countries require registration, which countries don’t and which countries don’t support Sender IDs at all, is to go to this page. Clicking on the individual country links will reveal best practice guidelines on how to send SMS traffic through that specific country.

IMPORTANT NOTE: If you use a Sender ID, you cannot receive message responses, so your use-case must be one-way only.

What Number/Sender ID Should I Use?

Clearly, there are lots of options to choose from. But deciding on which type of phone number or sender ID to use will depend mostly on your use-case. If you require high-volume, time-sensitive and most effective SMS deliverability, then using a short code is the right choice. If you are only interested in sending messages from your company name, and do not need to receive message responses, then try using a sender ID. Or perhaps you only send small volumes of traffic and do not want to invest in a short code, in this case, perhaps long codes might be your choice. Of course, using a Twilio Messaging Service will allow you to use a combination of these three, maximizing your chances for deliverability.  

Here’s a breakdown of your options: