Concatenated SMS: definition and how it works
Published and updated
A concatenated SMS is a message longer than one segment that the sender splits into several SMS carrying a shared header, so the receiving phone can reassemble them into one text.
How it works
A single SMS holds 140 octets of user data. Messages longer than that are handled by concatenation, specified in 3GPP TS 23.040, Technical realization of the Short Message Service. The sender splits the text into parts and prefixes each with a user data header that carries a reference number, the total number of parts and this part's index. The receiving handset collects parts with the same reference and shows them as one message.
The header costs space. It takes six octets of the 140, which is why a concatenated segment holds 153 GSM-7 characters instead of 160, and 67 UCS-2 characters instead of 70. A 161-character GSM-7 message is therefore two segments of 153 and 8, not 160 and 1.
Networks carry each part as a separate SMS. They can arrive out of order or seconds apart, and if one part is lost the phone shows the rest as fragments or nothing at all. Old or minimal handsets, and some carrier gateways, do not support reassembly and display each part separately.
Every part is billed. A cloud provider charges per segment, and a SIM plan counts each part against its allowance. That is why segment counting is a cost control, not a technicality: trimming a template from 165 characters to 160 halves its price.
- 3GPP TS 23.040, Technical realization of the Short Message Service (SMS), specifies the user data header used to concatenate short messages. portal.3gpp.org, checked on September 5, 2026
How this applies with textbee
textbee passes a long message to the phone, which splits it and sends the parts. The parts count as separate SMS on the SIM plan, and the phone sends them at its normal pace, so a long message also takes a little longer to leave.
Related terms
- SMS segment: An SMS segment is one physical text message of up to 140 bytes, the unit that networks carry and providers bill, so a long or non-Latin message counts as several segments.
- GSM-7: GSM-7 is the default 7-bit character set for SMS, defined in 3GPP TS 23.038, which fits 160 characters into the 140 bytes of a single text message.
- UCS-2: UCS-2 is the 16-bit character encoding SMS falls back to when a message contains any character outside the GSM-7 alphabet, which limits one segment to 70 characters.
Sources
- Concatenated SMS, portal.3gpp.org, checked on September 5, 2026