As per understand you are opening a comport of your Phone modem. and trying to communicate. I do see the comport configurations are incorrect because port 0 buadrate 0 is invalid.
I think you need to get some information about the how to communicate hardware with comport.
Second, when you are connect directly through the modem (not phone software). you need to use modem commands called AT commands
I have worked on this almost 7 years back, I did not remember correctly command for sending SMS, But I am giving below example you can try it.
Tip: before doing this in the C# code use and Terminal window ,I used hyperterminal ( not available after xp, but you can download exe from web). you can test this commands and everything is OK. Then start codeing in C#.