One curly apostrophe can triple an SMS bill. This page shows how the two encodings work, which characters force UCS-2, and how to stay on GSM-7. Paste a message below to test it.
Auto stays on GSM-7 until a character falls outside it. GSM-7 is 160 characters, then 153. UCS-2 is 70, then 67.
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GSM-7 · 160 left in this segment
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Twilio’s listed rate leaves out carrier fees. A2P registration, toll-free verification, and pass-through charges can add more. Carrier fees
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Say your appointment-reminder template is 150 characters of plain text. In GSM-7, that's 1 segment → $0.0083 per send at Twilio US long-code rates.
Now your marketing manager copies the template from Google Docs and the apostrophe in "You're" gets pasted as a curly quote (’ = U+2019). The message is now UCS-2. 150 characters / 67 per segment = 3 segments → $0.0249 per send.
If you send 100,000 reminders per month: the curly quote costs you an extra $1,660 every month. And nobody on the team will ever notice — the message looks identical.
Any character outside this list will force your message to UCS-2. The extended set (bottom row) counts as 2 septets per character — so a single € uses up 2 of your 160 characters.
| Character | Name | Code point | Safe GSM-7 swap |
|---|---|---|---|
| ’ | Right single curly quote | U+2019 | ' |
| ‘ | Left single curly quote | U+2018 | ' |
| “ | Left double curly quote | U+201C | " |
| ” | Right double curly quote | U+201D | " |
| — | Em dash | U+2014 | - or -- |
| – | En dash | U+2013 | - |
| … | Horizontal ellipsis | U+2026 | ... |
| ´ | Acute accent | U+00B4 | ' |
| → | Right arrow | U+2192 | -> |
| 🎉 | Any emoji | U+1F300+ | No GSM-7 equivalent |
', U+201C, U+201D → ", U+2013, U+2014 → -, U+2026 → ....Blooio sends iMessage at one rate per message. Emoji and length do not change the segment count, because there isn’t one.
GSM-7 is the default 7-bit alphabet used by the SMS protocol. It packs 8 characters into every 7 bytes, which is why a single 140-byte SMS segment can hold 160 GSM-7 characters. The alphabet (3GPP TS 23.038) covers basic Latin letters, numbers, common punctuation, and a small extended set: € [ ] { } ~ ^ | \.
UCS-2 is a 16-bit Unicode encoding that supports every character in the Basic Multilingual Plane — emojis, accented letters outside the GSM-7 set, Chinese, Arabic, Cyrillic, Hebrew, smart quotes, em dashes, and so on. At 16 bits per character, a 140-byte SMS segment only holds 70 UCS-2 characters.
Any single character outside the GSM-7 basic + extended alphabet. The most common offenders: emojis (🎉, 😂), smart/curly quotes (', ', ", "), em and en dashes (—, –), ellipses (…), acute accents (´), and any non-Latin script. One offending character flips the entire message — there is no partial UCS-2 mode.
Per segment, the same — but UCS-2 fits roughly 44% as many characters per segment, so the same message costs 2× to 4× more. A 150-character message that fit in 1 GSM-7 segment becomes 3 UCS-2 segments (70 + 70 + 10 chars). At Twilio's US long-code rate of $0.0083/segment, that's $0.0249 instead of $0.0083 — a 3× cost overrun on every send.
Not really — the carrier picks the encoding based on the characters in your body. What you can do is sanitize your message before sending: replace curly quotes with straight quotes, em dashes with hyphens, ellipses with three dots, and avoid emojis. The Smart Encoding toggle on this page automates the most common replacements.
No. iMessage uses Apple's Push Notification network, not the SMS protocol — there are no segments and no encoding limits. You can send emojis, long messages, images, and attachments without cost overruns. The blue-bubble iMessage delivery is also significantly higher engagement than green-bubble SMS.