A standard GSM-03.38 text message is 160 characters long. 1 UNIT.
A standard non GSM-03.38 text message (e.g. Unicode UCS-2 characters like Chinese or Arabic) is 70 characters long. 1 UNIT.
If the message is longer than these limits, it will concatenate and be sent as 2 UNITS (or more, up to a limit of 10 UNITS).
Note: If you compose your message in a different App e.g. MS Word and then cut and paste into the UI or API interface this can result in the content being interpreted as Rich Text and change the format from GSM to non GSM. If this happens it can cause higher than expected message charges.
When concatenation occurs the first message reduces to 153 characters (GSM) or 67 characters (non-GSM), and the remaining characters roll into a second message (concatenation). The reason for this is that the concatenation information is contained within the UDH and uses space within the SMS payload when concatenation occurs.
Any charge that applies to the message being sent will therefore per UNIT.
Note: The following GSM 0.038 characters cannot be included in your message: ¤¡§|
Campaign Manager UI will clearly show when a message becomes 'long' and you will have to acknowledge acceptance of the charges, before saving your message.
Email2SMS will limit sending to 1 'unit' by default, unless you change the default to something higher (in the 'domains' tab). See: Enabling Concatenation in Email2SMS
Pager Messages (NZ Only) 1 Unit is 240 characters long, otherwise, same rules apply.
REST Email (API) 1 unit is 'unlimited' characters, the unit is charged on the send.