# 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[](#syncing-phone-numbers-senders-to-customerio)

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)

## Using a Manual Sender ID[](#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-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[](#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.