> This page is part of the [Customer.io documentation](https://docs.customer.io). For the complete index, see [llms.txt](https://docs.customer.io/llms.txt).
> Last updated: July 10, 2026

# SMS sender numbers

When you enable SMS in Customer.io, we’ll sync your phone numbers and short codes. This page explains a bit more about how to add new phone numbers so you can select different senders for different messages.

## Syncing Phone Numbers (Senders) to Customer.io

If you add or change any of your sender identities in your Twilio account, you’ll need to re-sync them in Customer.io before you’ll see your changes in Customer.io.

Go to **[\> Workspace Settings > SMS](https://fly.customer.io/workspaces/last/settings/actions/twilio)** and click **Sync from Twilio**.

[![The Customer.io Twilio Settings page where you can sync your sender identities from Twilio.](https://docs.customer.io/images/twilio-sync-senders.png)](#36be948e9d428d4b04aaa51080577f34-lightbox)

### Hide auto-synced sender identities

When you sync from Twilio, Customer.io automatically imports all of your sender identities. If you don’t want to use some of these auto-synced senders, you can hide them. Hiding a sender moves it to a separate **Hidden** tab on your SMS settings page and prevents it from appearing as an option when you draft a message. Hiding a sender doesn’t remove it from Twilio—you can unhide it at any time to make it selectable again.

Go to **[\> Workspace Settings > SMS](https://fly.customer.io/workspaces/last/settings/actions/twilio)** and click **Hide** next to sender identities you don’t want to use.

## Using a Manual Sender ID

You’ll see *Manual Sender IDs* in your Twilio Settings. You can add an Alphanumeric Sender ID, a Message Service ID, or provide some Liquid that dynamically determines the Sender ID for each message here.

[![twilio_config.png](https://docs.customer.io/images/twilio_config%282%29.png)](#94fcddd413949fb37f3fc85c8a08cc8a-lightbox)

## Alphanumeric ID

Alphanumeric IDs can help your messages stand out, but they have a few quirks:

*   **They’re one-way**: Your customers cannot reply to them.
*   **Opt-in/opt-out**: Customers must opt into messages from your ID, and be informed on how to opt out.
*   **Alphanumeric IDs aren’t supported in all countries, including the USA**: If you try to send to an [unsupported country](https://support.twilio.com/hc/en-us/articles/223133767-International-support-for-Alphanumeric-Sender-ID) from an Alphanumeric Sender ID, your message will fail to send.

### Set up an alphanumeric ID

1.  [Enable alphanumeric IDs in Twilio first](https://support.twilio.com/hc/en-us/articles/223181348-Getting-started-with-Alphanumeric-Sender-ID)! You can add alphanumeric senders in Customer.io, but if you haven’t enabled the feature in Twilio, messages using your alphanumeric sender will fail.
    
2.  Go to **[\> Workspace Settings > SMS](https://fly.customer.io/workspaces/last/settings/actions/twilio)** and click **Add Sender ID**.
    
3.  Enter your *Sender ID* and the *Name* you’ll use to refer to your sender.
    
    *   **Name**: this is how you’ll refer to the ID internally; your customers won’t see this.
    *   **Sender ID**: You can use both upper- and lower-case ASCII letters, digits 0 through 9, and spaces in your ID. Your ID must contain at least one character that isn’t a number.

*   *   [Syncing Phone Numbers (Senders) to Customer.io](#syncing-phone-numbers-senders-to-customerio)
        *   [Hide auto-synced sender identities](#hide-auto-synced-sender-identities)
    *   [Using a Manual Sender ID](#using-a-manual-sender-id)
    *   [Alphanumeric ID](#alphanumeric-id)
        *   [Set up an alphanumeric ID](#set-up-an-alphanumeric-id)

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