Plain text - 7-bit encoding
The message length for 7bit encoding is up to 160 characters.
153 chars - Multipart SMS
Unicode Encoding
Unicode (UCS-2) encoding supports a great range of characters and languages compared to the very limited alphabet of 7bit encoding.
If your message contains any characters not listed in the 7-bit alphabet, UCS-2 encoding is automatically used. In this case, each message takes up a lot more space, thus the message length is reduced to 70 characters.
67 chars Multipart SMS