Step 1) Do a little research. Google is a good start point (i.e.
How to recieve sms from USB Modem(GSM Modem) using C#.[
^])
Step 2) Start coding
Step 3) Compile and use the debug to solve little issues
Step 4) When you get a problem you don't know how to solve
but at least you tried it, then come back and ask for something concrete with a snippet of the code giving problems
Sorry if this is not the answer you were looking for. But your question is a bit too wide to be answered at the "Quick" Answers. It is better and you get faster help if you make 10 concrete questions about concrete problems, than a big question about a "how-to guide"
In addition, you might want to read:
What have you tried?[
^] so you can know how to get better answers next time
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