Auto dial GSM USB modem for internet connect and disconnect from C#/VB.net

Question

Hello Everybody,
I want to know, how to access USB modem of any company like IDEA,TATA through C#/VB.net programming. And how to allow program to connect internet through modem connected and also disconnect from internet.
If anyone know any single hint regarding above concept implementation,please let me know. Suggestion also welcomed.