Each message you send or receive consist of segments. Each segment counts as 1 Pony Express message credit.
A segment counted as 160 characters (140 bytes) encoded as GSM 03.38 character set. If a message contains characters, not in GSM 03.38 character set, UCS-2 character set will be used and the number of segments might be higher.
The amount of data you can squeeze into a single SMS message is limited – typically 140 bytes, or 160 characters for standard GSM encoding.
Message credits let you exceed that limit by breaking the message into parts and reassembling it on the receiving end.
Emojis & special characters matter: Characters outside of the standard GSM set (like emojis) are automatically encoded as UCS-2. UCS-2 uses more bytes per character, limiting you to 70 for a single message and 67 characters for longer ones.