SMS Segments
When using any SMS bulk messaging system, including via Magpi, it is important to understand that your messages may be of a different length than is apparent: there may be hidden characters or other considerations that cause messages to break unexpectedly, or to come out of order. One of the issues is the number of segments needed to transport your messages. This can be a complex topic, but the experts at Twilio (one of the systems Magpi uses to send SMS messages) have crafted a useful article: What the Heck is a Segment.
Segment Calculator
To see how many segments are needed for each of your messages, and where the messages will break, you can paste them into this calculator.
SMS Character Sets
When you want to send an SMS message, whether by itself or as part of a structured SMS or iSMS activity, you'll need to understand that there are two different sets of characters that are used by different mobile carriers:
1 - GSM
Many mobile networks limit text messages to the 128 character GSM character set (full list here). When using this set, a text message can contain 160 characters.
There are also 10 "extended GSM" characters, which use two 7-bit characters (ESC followed by another character). An example is the Euro symbol: €. If you use any extended GSM characters, it will take up two, not one, of the 160 character limit.
2 - UCS2
If you need to send characters that aren't in the GSM character set, you'll need to use UCS-2 character set. UCS-2 allows you to send most common characters that you could type on your computer (which uses unicode character set), but each UCS-2 character takes up twice as much memory as a GSM character. That means that if you use any UCS-2 characters (full list here), your text message can only include 70 characters, not 160.