I have one of these modems & mine works very well. Minicom is a great way to test it, also.
This modem is capable of a DTE rate of up to 230400, but your 57600 selected speed is fine for testing.
Your Init string should be: ATZ4 - this is the USR standard reset string which will enable hardware handshaking.
If your intent is to connect to the Internet, minicom won't do that for you. minicom will let you communicate with the modem, dial a number, and generally test the modem.
For the Internet you'll need a "dialer program". wvdial is already installed and works quite well. In order to use it, you'll need to edit the file:
You can (as root) edit your /etc/wvdial.conf file to look like this, then, in a terminal, type:
New PPPD = yes
Stupid Mode = yes
Modem Type = Analog Modem
ISDN = 0
Auto DNS = 1
Auto Reconnect = 0
Modem = /dev/ttyACM0
Baud = 230400
Init1 = ATZ4
Phone = 503 742 9199
Username = WhoIsThis
Password = Guessit
after entering the root password, your modem should dial & connect.
After we get this working, we can work on fancier or easier ways to connect. But we'll stick to the basics for now in order to get things running.