The amount of data that can fit into a single SMS message is limited – typically 140 bytes, or 160 standard characters. Message segments let you exceed that limit by breaking the message into parts and reassembling it on the receiving end.
Often, this reassembly process puts the messages back together correctly for the recipient. Occasionally, however, a receiving carrier might deliver the message in segments, and may even deliver them out of order. This is why Textline has a 320-character limit in place for messages to individual contacts, and a 160-character limit in place for Announcements - it helps to mitigate any potential confusion on the receiving end of a message.
We recommend keeping your messages as short as possible - SMS stands for Short Message Service, after all!
A few notes on message segments:
1. For messages between 160-320 characters, we will handle the segmentation part for you and will automatically encode and segment your messages, reassembling them on the recipient's device whenever possible.
2. Message reassembly requires that the downstream carrier support concatenation. If not, your message may be delivered in multiple parts. Again, this is why we recommend keeping messages short!
3. Emojis & special characters - characters outside of the standard GSM set - are automatically encoded differently by Twilio, and use more bytes per character.
You can find more information on segments in Twilio's blog, here!