South Korea SMS Best Practices, Compliance, and Features

South Korea SMS Market Overview

Market Conditions: South Korea has one of the world's most advanced mobile markets, with nearly 100% smartphone penetration. The market is dominated by three major mobile operators: SK Telecom, KT (Korea Telecom), and LG U+. While OTT messaging apps like KakaoTalk are extremely popular for personal communications, SMS remains crucial for business communications, particularly for authentication, notifications, and marketing. Android devices hold approximately 70% market share, with iOS devices making up most of the remainder.

Key SMS Features and Capabilities in South Korea

South Korea maintains strict regulations on SMS capabilities, with specific requirements for message formatting, sender IDs, and delivery mechanisms to ensure security and prevent spam.

Two-way SMS Support

Two-way SMS is not supported in South Korea for A2P (Application-to-Person) messaging. Businesses must use one-way messaging for their communications, with alternative channels required for customer responses.

Concatenated Messages (Segmented SMS)

Support: Concatenated messages are no longer supported by most carriers, with SK Telecom being the only exception.
Message length rules: One SMS segment can contain up to 140 bytes, equivalent to 140 ASCII characters or 70 Unicode characters.
Encoding considerations: Messages support both GSM-7 (ASCII) and UCS-2 (Unicode) encoding, but must use EUC-KR encoding for Korean characters.

MMS Support

MMS messages are automatically converted to SMS with an embedded URL link. This ensures compatibility across all carriers while still allowing rich media content to be shared through a web-based approach.

Recipient Phone Number Compatibility

Number Portability

Number portability is available in South Korea, allowing users to keep their phone numbers when switching carriers. This feature does not significantly impact message delivery or routing as the infrastructure is well-established.

Sending SMS to Landlines

Sending SMS to landline numbers is not possible in South Korea. Attempts to send messages to landline numbers will result in a 400 response error (code 21614), and the message will not be delivered or charged to the account.

Compliance and Regulatory Guidelines for SMS in South Korea

SMS communications in South Korea are regulated by the Korea Communications Commission (KCC) and Korea Internet & Security Agency (KISA). Organizations must comply with the Personal Information Protection Act (PIPA) and the Act on Promotion of Information and Communications Network Utilization and Information Protection.

Consent and Opt-In

Explicit Consent Requirements:

• Written or electronic consent must be obtained before sending marketing messages
• Consent records must be maintained for at least 3 years
• Consent forms must clearly state the purpose, frequency, and type of messages

Best Practices for Consent:

• Implement double opt-in verification
• Maintain detailed consent logs with timestamps
• Provide clear terms and conditions in Korean
• Regular consent renewal every 2 years

HELP/STOP and Other Commands

• All marketing messages must include opt-out instructions in Korean
• Standard commands include:
  • "수신거부" (Opt-out)
  • "도움말" (Help)
• Commands must be free of charge for users
• Response to opt-out requests must be processed within 24 hours

Do Not Call / Do Not Disturb Registries

• South Korea maintains a national Do-Not-Send Registry managed by KISA
• Businesses must:
  • Check numbers against the registry monthly
  • Maintain internal suppression lists
  • Honor opt-outs immediately
  • Document compliance procedures

Time Zone Sensitivity

• Standard sending hours: 08:00 to 21:00 KST
• Emergency notifications exempt from time restrictions
• Avoid sending during major holidays like Seollal and Chuseok
• Consider business hours (9:00-18:00) for B2B communications

Phone Numbers Options and SMS Sender Types for in South Korea

Alphanumeric Sender ID

Operator network capability: Not supported Registration requirements: N/A Sender ID preservation: All sender IDs are converted to numeric format

Long Codes

Domestic vs. International:

• Domestic: Supported but requires local business registration
• International: Supported with prefix (009 or 006)

Sender ID preservation: No, international numbers are modified with country prefix Provisioning time: 3-5 business days Use cases: Transactional messages, alerts, notifications

Short Codes

Support: Not supported for international businesses Provisioning time: N/A Use cases: N/A

Restricted SMS Content, Industries, and Use Cases

Prohibited Content:

• Gambling and gaming
• Adult content
• Political campaigns
• Cryptocurrency promotions
• Unauthorized pharmaceutical products

Regulated Industries:

• Financial services require additional verification
• Healthcare messages must comply with medical privacy laws

Content Filtering

Carrier Filtering Rules:

• Messages must use approved character sets (EUC-KR)
• URLs must be from whitelisted domains
• Content screening for prohibited keywords

Tips to Avoid Blocking:

• Use registered sender IDs
• Avoid URL shorteners
• Include mandatory prefixes ([Web 발신] for A2P)
• Keep content clear and professional

Best Practices for Sending SMS in South Korea

Messaging Strategy

• Keep messages under 70 characters when possible
• Include clear call-to-action
• Use formal Korean language style
• Avoid excessive punctuation or emojis

Sending Frequency and Timing

• Limit to 1-2 messages per day per recipient
• Respect quiet hours (21:00-08:00 KST)
• Plan around Korean holidays
• Space out bulk campaigns

Localization

• Primary language: Korean (Hangul)
• Use formal business Korean (존댓말)
• Include English only when necessary
• Test character rendering across devices

Opt-Out Management

• Process opt-outs within 24 hours
• Maintain centralized opt-out database
• Confirm opt-out status to users
• Regular database cleaning

Testing and Monitoring

• Test across all three major carriers
• Monitor delivery rates by carrier
• Track opt-out rates
• Regular content compliance checks

SMS API integrations for South Korea

Twilio

Twilio provides a robust SMS API with specific support for South Korean messaging requirements.

import twilio from 'twilio';

// Initialize the client with your credentials
const client = twilio(
  process.env.TWILIO_ACCOUNT_SID,
  process.env.TWILIO_AUTH_TOKEN
);

// Function to send SMS to South Korea
async function sendSmsToKorea(
  to: string,
  message: string
): Promise<void> {
  try {
    // Format the phone number to E.164 format for Korea
    const formattedNumber = to.startsWith('+82') 
      ? to 
      : `+82${to.replace(/^0/, '')}`;

    const response = await client.messages.create({
      body: message,
      to: formattedNumber,
      // Sender ID will be automatically formatted with required prefix
      from: process.env.TWILIO_PHONE_NUMBER,
      // Optional: Specify validity period
      validityPeriod: 3600 // 1 hour
    });

    console.log(`Message sent successfully: ${response.sid}`);
  } catch (error) {
    console.error('Error sending message:', error);
    throw error;
  }
}

Sinch

Sinch offers dedicated APIs for the South Korean market with built-in compliance handling.

import axios from 'axios';

class SinchSmsService {
  private readonly apiToken: string;
  private readonly servicePlanId: string;
  private readonly baseUrl: string;

  constructor(apiToken: string, servicePlanId: string) {
    this.apiToken = apiToken;
    this.servicePlanId = servicePlanId;
    this.baseUrl = 'https://sms.api.sinch.com/xms/v1';
  }

  async sendSms(to: string, message: string): Promise<void> {
    try {
      const response = await axios.post(
        `${this.baseUrl}/${this.servicePlanId}/batches`,
        {
          from: '009xxx', // Will be automatically prefixed
          to: [to],
          body: message,
          // Required for Korean character support
          encoding: 'EUC-KR'
        },
        {
          headers: {
            'Authorization': `Bearer ${this.apiToken}`,
            'Content-Type': 'application/json'
          }
        }
      );

      console.log('Message sent:', response.data.id);
    } catch (error) {
      console.error('Sinch SMS error:', error);
      throw error;
    }
  }
}

Bird

Bird's API provides streamlined integration for South Korean messaging compliance.

import { BirdClient } from '@bird/sdk';

class BirdSmsService {
  private readonly client: BirdClient;
  private readonly channelId: string;

  constructor(accessKey: string, channelId: string) {
    this.client = new BirdClient(accessKey);
    this.channelId = channelId;
  }

  async sendMessage(
    phoneNumber: string, 
    messageText: string
  ): Promise<void> {
    try {
      const response = await this.client.messages.create({
        channel: this.channelId,
        recipient: {
          type: 'individual',
          phoneNumber: phoneNumber
        },
        content: {
          type: 'text',
          text: messageText
        },
        // Korea-specific options
        options: {
          region: 'kr',
          encoding: 'EUC-KR'
        }
      });

      console.log('Message sent:', response.messageId);
    } catch (error) {
      console.error('Bird SMS error:', error);
      throw error;
    }
  }
}

API Rate Limits and Throughput

• Default rate limits vary by provider:
  • Twilio: 100 messages/second
  • Sinch: 50 messages/second
  • Bird: 30 messages/second

Throughput Management Strategies:

• Implement exponential backoff
• Use queue systems (Redis/RabbitMQ)
• Batch messages when possible
• Monitor delivery receipts

Error Handling and Reporting

Common Error Scenarios:

• Invalid phone numbers
• Network timeouts
• Character encoding issues
• Rate limit exceeded

Best Practices:

// Example error handling implementation
async function handleSmsError(error: any): Promise<void> {
  if (error.code === 'INVALID_NUMBER') {
    // Clean number from database
    await cleanInvalidNumber(error.number);
  } else if (error.code === 'RATE_LIMIT_EXCEEDED') {
    // Implement backoff strategy
    await exponentialBackoff();
  }
  
  // Log error for monitoring
  await logger.error({
    error: error.message,
    code: error.code,
    timestamp: new Date(),
    service: 'sms'
  });
}

Recap and Additional Resources

Key Takeaways:

1. Always use EUC-KR encoding for Korean characters
2. Implement proper error handling and retry logic
3. Respect rate limits and implement queuing
4. Follow all compliance requirements

Next Steps:

1. Review the Korea Communications Commission guidelines
2. Implement proper consent management
3. Set up monitoring and reporting
4. Test thoroughly across all carriers

Additional Resources:

• Korea Communications Commission
• KISA Guidelines
• Telecom Business Act
• Personal Information Protection Act