An SMS is billed per segment, and the encoding decides how many characters fit in a segment. Understanding this keeps your messages - and your bill - lean.
GSM-7 vs Unicode
Plain text using the standard GSM alphabet is encoded as GSM-7: 160 characters per single segment. The moment your text contains a character outside that alphabet - many accented letters, most emoji, non-Latin scripts - the whole message switches to Unicode (UCS-2), which fits only 70 characters per segment.
How concatenation works
Longer messages are split into segments and reassembled on the handset. Concatenation headers reduce the per-segment limit to 153 (GSM-7) or 67 (Unicode). So a 300-character GSM-7 message is 2 segments; the same length in Unicode is 5.
Keep it to one segment
Avoid smart quotes and stray Unicode from copy-paste, keep links short with a URL shortener, and preview the segment count before you send. The eSMS composer shows live encoding and segment count as you type, so there are no surprises on the invoice.
Get started
See live segment counts as you write: try the composer.