Simply install the “wvdial” package and edit /etc/wvdial.conf:
[Dialer Defaults]
Phone = *99***1#
Username = username
Password = password
Stupid Mode = 1
Dial Command = ATDT
[Dialer hsdpa]
Modem = /dev/ttyUSB0
Baud = 460800
Init2 = ATZ
Init3 = ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0
ISDN = 0
Modem Type = Analog Modem
Then run “wvdial hsdpa” and you should be connected. I didn’t have to specify the Optus APN anywhere.