Glossary
What is Unicode SMS?
A Unicode SMS uses the UCS-2 encoding so it can carry emoji, curly quotes and non-Latin scripts, but one part then holds only 70 characters.
One character outside GSM-7 is enough to switch a whole text to Unicode. An emoji will do it, so will a curly apostrophe copied from an email, or a customer's surname with a Polish ł in it. The limit drops from 160 characters to 70 for a single part, and to 67 per part once the text is split. Most emoji take two of those places.
Take a Leeds salon's 120-character reminder. In plain text that's one part. Add a heart emoji to the end and it becomes a two-part Unicode text, which doubles the cost of the reminder for the sake of one picture. Fine for a birthday text, maybe, but probably not for a reminder.
The CaptiFi Connect composer tells you when a text has gone Unicode and lists the characters responsible, so you can decide whether to keep them. Unicode texts are billed the same way as any other, one credit per part to a UK mobile, and you'll see the part count before anything is sent.