I have a Tata Docomo sim with huawei e173 usb modem.Following is my /etc/wvdial.conf on Ubuntu 10.4.
Init1 = ATZ
Init2 = ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0
Password = internet
Phone = *99#
Modem Type = Analog Modem
Stupid Mode = 1
Init3 = AT+CGDCONT=1, "IP", "TATA.DOCOMO.INTERNETHVC"
Baud = 9600
New PPPD = yes
Modem = /dev/ttyUSB_utps_modem
ISDN = 0
Username = internet
Auto Reconnect = yes
Though officially (at the time of writing this) only Tata Docomo dongles are supported, and most probably you will get this reply from CC. Still a helpful soul at CC sms'd me this line
AT+CGDCONT=1, "IP", "TATA.DOCOMO.INTERNETHVC
rest is from other sources from Internet and auto generated. A good way is to run wvdialconf and then try to add the missing lines from above, rather than copy pasting whole file.
Hope that helps.