TL;DR
Concatenated SMS is a long text message split into multiple SMS segments that are reassembled on the recipient’s phone. It allows businesses to send messages longer than one segment, but each part may be billed separately and the available characters per segment are reduced.
At a glance
Question | Answer |
|---|---|
What is concatenated SMS? | A long SMS divided into linked message parts |
Why is it used? | To send messages longer than one SMS segment |
Is it billed as one message? | Usually no; each segment may be charged separately |
What affects the number of segments? | Encoding, character count, headers, and message content |
Does Unicode change the limit? | Yes. Unicode generally supports fewer characters per segment |
Can parts arrive separately? | They can, depending on device, carrier, and network conditions |
What is concatenated SMS?
A concatenated SMS is a long message that has been divided into multiple smaller SMS parts. Each part contains information that allows the receiving device to identify the message and display it as one continuous text.
The customer may see one long message in the messaging application, but the mobile network has transmitted several separate SMS segments.
For example:
The exact number depends on the character encoding and provider implementation.
Concatenation is also known as:
- Multipart SMS
- Long SMS
- Segmented SMS
- Multi-part message
Why are long SMS messages split?
Traditional SMS has a limited payload size. A single segment generally supports:
- Approximately 160 GSM-7 characters
- Approximately 70 Unicode characters
When a message exceeds the single-segment limit, the sending platform divides it into parts.
Each part needs a header that tells the receiving phone:
- The message belongs to a larger group.
- How many parts exist.
- Which part is being displayed.
- How the message should be reassembled.
Because of this additional information, concatenated messages have a lower character capacity per part.
Typical planning figures are:
Encoding | Single SMS | Concatenated SMS part |
|---|---|---|
GSM-7 | Approximately 160 characters | Approximately 153 characters |
Unicode | Approximately 70 characters | Approximately 67 characters |
These figures can vary by provider and message configuration.
How concatenated SMS works
A typical workflow is:
- The application creates the final message.
- The SMS platform detects the character encoding.
- The platform calculates the message length.
- The message is divided into segments.
- Each segment receives a linking header.
- The segments are submitted through the SMS gateway.
- The carrier and SMSC attempt delivery.
- The receiving phone reassembles the segments.
The message is not necessarily delivered as one network transaction. It is transmitted as multiple linked messages.
Helo.ai’s guide on how to send bulk SMS is useful for understanding how long messages, campaign templates, delivery reporting, and message costs interact.
What determines the number of SMS segments?
Character encoding
GSM-7 generally supports more characters per segment than Unicode. A message containing emojis, Indian-language text, or unsupported symbols may switch to Unicode and create more segments.
Message length
The longer the message, the more segments it requires.
Personalisation
Dynamic fields such as customer names, order numbers, dates, and addresses may increase the final length.
Message headers
Concatenation requires additional information, which reduces the available characters per part.
Provider implementation
Different providers may use different encoding detection, header, or segmentation rules.
Message type
Transactional and promotional SMS may have different templates, compliance rules, and content constraints.
Example of SMS segmentation
Consider two messages with a similar visible length.
Message A: GSM-7
If the message remains under the single-segment GSM-7 limit, it may be billed as one SMS.
Message B: Unicode
The message uses Unicode because it contains Hindi characters. A longer version may reach the multi-part threshold much sooner.
The customer may see the message as one continuous message, but the business may be charged for multiple segments.
How concatenated SMS affects cost
Concatenation can increase SMS cost because providers often charge by message segment rather than by the visible message.
For example:
The actual price depends on:
- Destination country
- Provider
- Carrier
- Message category
- Encoding
- Sender type
- DLT requirements
- Promotional or transactional classification
Before sending a large campaign, businesses should calculate the final segment count after all variables are inserted.
Concatenated SMS and India
Indian businesses should pay particular attention to concatenation because multilingual messages often use Unicode.
Messages in Hindi, Marathi, Tamil, Bengali, Telugu, Gujarati, Kannada, and Malayalam may require Unicode encoding. This generally reduces the number of characters available per segment.
Businesses should also consider:
- DLT-approved templates
- Entity registration
- Sender headers
- Consent
- DND requirements
- Promotional message time restrictions
- Template variables
- Operator filtering
Changing the language or message structure may require a different approved template.
Customer-experience risks
Although most modern phones reassemble concatenated SMS, problems may still occur:
- Parts arrive out of order.
- One segment fails while others arrive.
- The message appears incomplete.
- A customer sees the action only in a later segment.
- The link is separated from the explanation.
- Delays make the message difficult to understand.
- Older devices display segments separately.
For important notifications, place the critical information near the beginning and avoid splitting an OTP, payment amount, appointment time, or security instruction across several parts.
Best practices
- Keep important messages short.
- Calculate the final segment count.
- Detect GSM-7 or Unicode automatically.
- Insert variables before counting characters.
- Keep links short and recognisable.
- Place the CTA early.
- Avoid unnecessary emojis.
- Test every language version.
- Test delivery on several devices.
- Monitor segment-level cost.
- Use a fallback channel for critical alerts.
- Review DLT templates before launching in India.
For promotional campaigns, review Helo.ai’s promotional SMS guide to align message length with campaign structure and compliance requirements.
How developers should implement concatenation
A production SMS platform should expose:
- Encoding type
- Character count
- Segment count
- Message ID for each part
- Group or concatenation ID
- Delivery status
- Failure reason
- Estimated charge
- Final delivery outcome
The application should not assume that one API request equals one billable SMS. One request may create multiple network segments.
Developers should also make sure that retries do not resend only one part of a concatenated message. A retry should preserve the message grouping and avoid creating duplicate or incomplete content.
Common mistakes
Counting visible characters only
Encoding affects the real capacity of each segment.
Counting before personalisation
Dynamic variables can increase the length or change the encoding.
Treating the message as one billable unit
The recipient may see one message, but the provider may charge for multiple segments.
Placing the CTA at the end
Customers may not see the action if later segments are delayed or missing.
Using unsupported symbols
Smart punctuation, emojis, and special characters can trigger Unicode.
Not testing fallback
An incomplete or poorly formatted message may be delivered when the rich or preferred version is unavailable.
Frequently asked questions
What is a concatenated SMS?
It is a long SMS divided into multiple linked parts that the recipient’s phone attempts to display as one message.
Is concatenated SMS charged as one message?
Usually, no. Each SMS segment may be billed separately, depending on the provider and destination.
How many characters fit in a concatenated SMS?
A GSM-7 segment generally supports around 153 characters when concatenated. A Unicode segment generally supports around 67 characters. Exact limits may vary.
Does Unicode create more SMS segments?
It can. Unicode generally has a lower character capacity per segment than GSM-7.
Will the recipient see multiple messages?
Modern devices usually reassemble the parts, but the experience can vary by device, carrier, network, and delivery order.
Can a concatenated SMS contain an OTP?
Yes, but OTP messages should be kept as short as possible. The code and security instruction should not depend on a later segment.
How can I reduce concatenated SMS costs?
Shorten the message, remove unnecessary characters and emojis, use GSM-7 where appropriate, reduce variable length, and calculate the final segment count before sending.
Does concatenated SMS affect delivery speed?
It can. Multiple segments may experience different carrier or network conditions, and one delayed part can affect the complete customer experience.