A standard SMS contains at most 160 characters (note: the limit is 70 characters when sending Unicode messages). Even though text messages are limited in length, most mobile handsets can display messages longer than the text limit. To the sender and receiver, it is a seamless user experience and feels like you are sending and receiving entire messages at once regardless of the length. In order to ensure that long messages are delivered in its entirety, the SMS service provider needs to support the automatic splitting and concatenation of long SMS messages.
Plivo’s Message API supports long SMS concatenation and automatically splits long SMS text messages into multiple SMS and adds a concatenation header to each message so that it can be stitched together (i.e., concatenated) at receiver’s mobile device. Though, some carriers and handsets do not support long SMS concatenation.