Comment 12 for bug 874900

Here is a workaround to auto start a mobile broadband connection after user login:

In the command line list the configured connections in your Network Manager:
$ nmcli con list
NAME UUID TYPE TIMESTAMP-REAL
Tele2 Default 1 93c93207-adce-40e4-beb5-d9f9c830d474 gsm Sat 25 Feb 2012 01:27:42 PM CET
Vipnet connection 1 054bdd1f-34e3-4db1-b18b-d38e885276c8 gsm never

The first item in a row is the connection name.
Now, create a command script that starts one of your connections after a delay of e.g. 10 seconds (maybe you'll need a longer delay if your broadband device needs more time to initialize):

#!/bin/sh
sleep 10
nmcli nm wwan on
nmcli con up id "Tele2 Default 1"

If the connection is used by multiple users on your Ubuntu, you can put the lines in a file accessible to all users, e.g.
 /usr/local/bin/start_my_connection
and set the file permissions as follows:

$ sudo chmod 775 /usr/local/bin/start_my_connection

Finally, configure starting the script after login: in Startup Applications Preferences add an item and enter the script path (/usr/local/bin/start_my_connection) as the program command.