Senior project, no one here will give you codes. The whole point of it is to get you to figure it all out. Hopefully, you haven't waited until the last week to do it.

This library should let you connect with a usb modem I believe. (unsure, never used it, it might be for serial modems)
http://java.sun.com/products/javacomm/

If that doesn't do what you need, ask your teacher which library gives that support. If you're expected to write this support on your own, you'll need to use JNI and a DLL made in C++ to interact with hardware devices like that.

There's also jUSB on sourceforge, but I don't know how complete the project is yet.