There is already an
answer[
^] about the issue.
Anyway to send multipart SMS you have to use the
PDU mode[
^].
A sample for multipart PDU is
here[
^] where they show you how to add an UDH (User Data Header) to send a multipart message in PDU mode.
There are a lot of online PDU encoders just
google[
^].
There is an excellent
article wiith code for a library[
^] on codeproject.