# Long-code

A Long-code Sender ID is an eligible DID phone number used to send A2P SMS messages. Recipients see the DID number as
the message sender. Long-code Sender IDs can also support two-way messaging.

## Common uses

Use a Long-code Sender ID when recipients should see a consistent DID number or need to reply. Common uses include:

- Two-way customer support and conversations.
- Appointment and delivery updates that allow replies.
- Account and service notifications sent from a consistent phone number.
- US A2P messaging that requires 10DLC registration.

## How messages appear

Recipients see the approved DID number as the message sender. Using the same number for related messages helps
recipients recognize the sender and follow the conversation.

[![Example message from a Long-code Sender ID with instructions to reply STOP to unsubscribe or HELP for assistance.](../../../_images/long-code.webp)](../../../_images/long-code.webp)


**Fig. 1.** Example message from a Long-code Sender ID.

## Messaging and replies

Recipients can reply to messages sent from a Long-code Sender ID when two-way messaging is supported. To receive their
replies, use a DID number that
supports inbound SMS and assign it to an inbound SMS trunk. Support for replies varies by destination country and mobile
network.

## Relationship with DID numbers

A Long-code Sender ID is a DID number assigned to the DIDWW account. Before
including the number in a verification, either
[purchase the number](../../../phone-numbers/buy-numbers/index.html) or
[port an existing number to DIDWW](../../../phone-numbers/number-porting/index.html).

The number must be active and available in [My Numbers](../../../phone-numbers/my-numbers/index.html), and support
**Outbound A2P SMS**. See the [supported feature filters](../../../phone-numbers/buy-numbers/filters-reference.html).

A DID number already assigned to another Sender ID Verification cannot be
selected for a new verification.

## Availability

Long-code Sender ID availability varies by country.

Check current availability on the [DIDWW website](https://www.didww.com/services/two-way-sms/a2p-messaging) or view the
available verification options in the [DIDWW User Panel](https://my.didww.com/#/sender_id_verifications/get_started).

## Verification requirements

Each DID number must be included in an approved Long-code verification before use. The verification associates the
selected DID numbers with the business, target country, and messaging use case submitted for review.

The Sender ID, business identity, message content, consent process, and and messages sent must meet the requirements of
the destination country.

To submit a verification, see [Create Long-code Sender ID
Verification](../how-to-guides/create-long-code-verification.html). For required submission fields, see [Long-code
verification](../sender-id-verification-reference.html#long-code-verification-reference).

## US A2P 10DLC registration

Application-to-person traffic sent to United States recipients using a 10-digit long code requires US A2P 10DLC
registration. The registration associates the business, use case, consent process, sample messages, and selected
numbers.

The submitted information must match the actual business and messaging use case. Consent must be collected directly for
the specific campaign. The sample
messages, website, privacy policy, terms of service, and opt-out process must also describe the same brand and messaging
use case.

To register eligible 10-digit long-code DID numbers, see [Create US 10DLC
Verification](../how-to-guides/create-us-10dlc-verification.html). For required US submission fields, see [United States
10DLC business information
fields](../sender-id-verification-reference.html#us-10dlc-verification-reference-business-information).

## Using a verified Sender ID

After the verification becomes [Active](../sender-id-verification-reference.html#sender-id-verification-statuses), the
selected DID numbers can be used as Sender IDs. Associate the verification with an outbound SMS trunk
and send only messages that match the approved business, destination country, and messaging use case.

For sending instructions, see [Send SMS using verified Sender
ID](../how-to-guides/send-sms-using-verified-sender-id.html) or the [HTTP
Specification](../../sms-trunks/technical-data/http-specification.html).

## Related resources

- [Create Long-code Sender ID Verification](../how-to-guides/create-long-code-verification.html)
- [Create US 10DLC Verification](../how-to-guides/create-us-10dlc-verification.html)
- [Sender ID Verification reference](../sender-id-verification-reference.html)
- [Sender ID content requirements](../compliance-content-requirements.html)
- [Sender ID types](index.html)

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