OneSignal provides the following ways to add phone number records into your account:

Import Option	Details
Dashboard Upload	Best if you have a CSV list of phone numbers and want to upload through the dashboard without code.
API Add a device	Use the Add a device endpoint to set the `device_type = 14` and the `identifier` as the phone number in E.164 format. Any other data you want to add is optional.
SMS SDK Methods	Can be used for long-term implementation on the client side.
Email & Phone Number Web Prompt	A web prompt that allows user to include their own phone number and email address.

Import Phone Numbers through Dashboard

Navigate to Audience > All Users > Update/Import Users

Select Upload CSV next to "Import phone_number(s)".

Import Phone Number CSV columns

Property	Details
`phone_number`	Required: must be in the E.164 format
`external_user_id`	Required: identifier that can be used to uniquely identify a user. See External User Ids for more details.

If you need help ensuring your CSV is in the correct format, download our template using CSV Template download button.

Note: The first row should have the column labels exactly matching the above Property names. The order does not matter.

You can automatically create a new segment for the imported list. This adds a tag to the newly imported list and auto-creates a segment based on the input value. For example, "SMS_Subscriber_Test_List" in the above image.

Once you Confirm and Import, you will get an email with the results from the CSV Import.

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You cannot have multiple phone numbers associated with an external_user_id. If the external_user_id exists, then we will replace the old phone number with the new one.
You cannot have the same phone number associated with multiple external_user_id. Only the last provided external_user_id will be linked with the phone number.
Please reach out to OneSignal support if you prefer to have multiple phone numbers for a given external_user_id.

Update User Records

To add or update custom attributes for the Phone Number records, keep the current CSV and add additional columns for tags. See Importing User Attributes or Tags for more details.