Glossary
What is Concatenated SMS?
A concatenated SMS is a long text sent as several linked parts, each with a small header so the receiving phone can join them back into one message.
SMS was built for short messages, so anything longer is cut into parts. Each part carries a user data header with a reference number, the total number of parts and its own position, and the phone uses that to rebuild the message in order, even if the parts turn up a second or two apart. The header takes six bytes of every part, which is why a split plain text holds 153 characters per part where a single text holds 160.
A letting agent in Cardiff texting a tenant 300 characters about a boiler engineer's visit sends two parts (153 and then 147) and the tenant sees one text on their phone.
CaptiFi Connect does the splitting for you, up to 10 parts, which is 1,530 plain characters or 670 in Unicode. You'll see the part count before you send, and each part uses one credit.