sudo wvdial reports:

--> WvDial: Internet dialer version 1.61
--> Cannot get information for serial port.
--> Initializing modem.
--> Sending: AT+CGDCONT=1, "IP", "telstra.internet"
OK
--> Modem initialized.
--> Sending: ATDT*99#
--> Waiting for carrier.
CONNECT 21000000
--> Carrier detected.  Starting PPP immediately.
--> Starting pppd at Sat Mar  3 09:21:43 2012
--> Pid of pppd: 1965
--> Using interface ppp0
--> Disconnecting at Sat Mar  3 09:21:45 2012
--> The PPP daemon has died: A modem hung up the phone (exit code = 16)
--> man pppd explains pppd error codes in more detail.
--> Try again and look into /var/log/messages and the wvdial and pppd man pages for more information.
--> Auto Reconnect will be attempted in 5 seconds
--> Cannot get information for serial port.
--> Initializing modem.
--> Sending: AT+CGDCONT=1, "IP", "telstra.internet"
OK
--> Modem initialized.

It then repeats the above a number of times.

^CCaught signal 2:  Attempting to exit gracefully...
--> Disconnecting at Sat Mar  3 09:21:49 2012

I have tried both telstra.bigpond and telstra.internet, makes no difference.


Roger


It sounds like you are making some progress at least.  I came across this while looking for more information:

http://us.generation-nt.com/answer/sierra-aircard-312u-not-connecting-help-203152682.html

Which basically says that the usb device address is incorrect and needs to be changed.  

Try using different USB device files in /etc/sysconfig/network-scripts/ifcfg-ppp0

The line of interest is MODEMPORT=/dev/ttyUSB3
 
See if maybe ttyUSB0, ttyUSB1, or ttyUSB2 work instead (provided it is using ttyUSB3).


thanks for your help, I just checked , there is no  /etc/sysconfig/network-scripts/ifcfg-ppp0 in ubuntu.
Roger