After successfully getting an Internet connection using Prolink PHS100 here, my brother needs to use Huawei E160 with that laptop. It turned out that for Huawei, /dev/ttyUSB0 should be used. The steps are just as follows:

1. Fire `sudo aptitude install wvdial' if you don't have it installed yet.
2. Save the following text as /etc/wvdial.conf and adjust `indosatm2', the phone number, the username and the password accordingly:

Modem = /dev/ttyUSB0
Baud = 115200
Modem Type = USB Modem
Init2 = ATZ
Init3 = ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0
Init4 = AT+CGDCONT=1,"IP","indosatm2"
Dial Command = ATDT
Phone = *99#
Username = ...
Password = ...
Stupid Mode = yes

3. Install usb-modeswitch 1.1.1 by downloading the code, extracting it, going to the extracted directory and firing `sudo make install'.
4. Plug the modem in.
5. Wait for about 1 minute. While waiting, repeatedly fire `ls /dev/ttyUSB*'. Once `ls' returns some files instead of saying "No such file or directory", you can go to step 6. If `ls' returns no file after 1 minute, unplug the modem, fire `sudo rmmod option' and go back to step 4.
6. Turn off NetworkManager by firing `sudo /etc/init.d/NetworkManager stop' (c.f., http://developer.pidgin.im/ticket/8545).
7. Fire `sudo wvdial', and if everything is okay, you should see an output like this. For subsequent use of the modem after the modem is unplugged or the machine is restarted or powered off, you only need to start from step 4.