How Encoding Hurts SMS Delivery Rate Benchmarks: GSM-7, UCS-2, and Emojis

You write a 140-character marketing message. You add a single emoji to make it pop. Your SMS provider just tripled your bill, and your delivery rate just tanked. Why? Because that emoji forced your message from GSM-7 encoding into UCS-2, fragmenting it into three separate messages.

The 160 vs. 70 Character Trap (GSM-7 vs UCS-2)

Why Vietnamese and Thai Characters Trigger Multi-Segment Billing

Standard English text uses GSM-7 encoding (160 characters per segment). However, Vietnamese diacritics and Thai characters require UCS-2 encoding, slashing the limit to just 70 characters per segment. As documented by Twilio's developer guides, the entire message converts to Unicode the moment a single unsupported character is detected.

How Concatenation Reduces the Actual Character Limit

When a message is split, the carrier adds a User Data Header (UDH) to reassemble it. This header eats up 6-7 characters per segment. So, a "70-character" limit is actually 63 characters for the first segment, and 67 for subsequent ones. A 200-character Vietnamese SMS becomes 4 segments, quadrupling your telecom costs.

 The Psychological Impact on Click-Through Rates

 How a Split Message Ruins the CTA

If your message is split, the user might receive the promotional text first, and the link or Call-to-Action (CTA) in the second message minutes later. Research by MessageBird (Bird) shows that split messages see an average drop in CTR of 40% compared to single-segment messages, as the psychological flow is interrupted.

 Best Practices for OTP and Marketing Copy Design

Keep OTPs strictly under 60 characters. For marketing, use URL shorteners cautiously and avoid emojis if your target audience uses non-Latin alphabets. Use the GSM-7 character counter before sending.

Technical Fixes for High Delivery Rates

Testing Templates Before Bulk Sending

Always test your templates with a character counter that accounts for Unicode conversion. Send a test to a local device in the target country (e.g., a TrueMove number in Thailand) to see exactly how it displays and how many segments it consumes.

Using RCS for Rich Media to Bypass Text Limits

If you need to send images or long-form content, use RCS Business Messaging. RCS supports rich media without the 160-character penalty, and falls back to SMS only if the device isn't supported. According to GSMA's RCS forecasts, this channel is quickly becoming the default for rich gaming updates.

Frequently Asked Questions

Q1: Does an emoji change my SMS pricing?
Yes. It forces UCS-2 encoding, reducing your limit to 70 characters and increasing the number of billable segments by 2-3x.

Q2: Why did my long SMS get cut off?
It likely exceeded the 160-character (GSM-7) or 70-character (UCS-2) limit without your provider properly handling segmentation.

Q3: How do I send Vietnamese text without splitting the message?
You must design shorter messages (under 63 characters) or use OTT channels like Zalo when rich text is required.

Q4: Can I remove the User Data Header (UDH) to save characters?
No. The UDH is added automatically by the SMSC to allow the receiving handset to reassemble the message. Without it, the message would arrive as disconnected fragments.

Q5: Why do some providers charge differently for Unicode messages?
Because Unicode messages generate more data payload for the carrier. Each UCS-2 segment has a different SS7 signaling cost than a GSM-7 segment, which providers pass down to you.

Data Sources

1. Twilio: How SMS Character Limits Work

2. GSMA: RCS Business Messaging Forecast 2026

3. MessageBird (Bird): SMS Marketing Benchmarks

Correction Contact: service@laaffic.com or +63 9637902308.
Published: 2026-11-09 | Last Updated: 2026-11-09