Glossary
What is SMS part?
An SMS part, or segment, is the most text one SMS can carry (160 plain characters, or 70 with Unicode); longer texts go out as several parts.
The 160 figure dates back to how GSM networks were designed, and it still decides what a text costs. Go over it and the message is split, with each part giving up a few characters to a small header that tells the phone how to put the pieces back together. That's why a long plain text holds 153 characters per part. The person receiving it sees one message.
Say a garage in Bristol sends 'Hi Sam, your MOT is booked for Thursday at 9:30...' and the finished reminder runs to 170 characters. That's two parts, so the garage pays for two texts, even though Sam only sees one.
In CaptiFi Connect one credit pays for one part to a UK mobile, so a two-part text costs two credits. The Send SMS page counts characters, parts and credits as you type and points out any character that's forcing Unicode, which is usually where the surprise extra part comes from. A single text can run to 10 parts.