You have asked in the wrong newsgroup. This newsgroup only deals with the C++
programming language (questions about classes, functions, operators, and
suchlike), not about particular problem (like communication with GSM modems). As
you didn't state which OS you are developing for (linux, win32, ...), we cannot
even say which newsgroup would be more appropriate for your question. Finding
the right newsgroup for your question is a non-trivial task, so you cannot
expect us to do this for you (all we can say is that you're off-topic in this
newsgroup).
Regards,
Stuart