1. Make sure wvdial is installed.
2. Gnome-ppp and KPPP are two good PPP dialers, but Gnome-ppp was not able to connect in at least 20 trials. KPPP works very well.
3. Connect the 3G phone, or the Aircard. (I have used Nokia 6263, and Sierra wireless 881U aircard)
3. Start a terminal, and type sudo wvdialconf. If would find the modem and write modem speed, device address, and other initial configuration in /etc/wvdial.conf.
4. Edit /etc/wvdial.conf to add :
Init3 = at+cgdcont=1,"IP","epc.tmobile.com" (epc.tmobile.com is only for T-Mobile, search Google for other providers' APN)
Phone = *99#
Username = user
Password = pass
Save the file.
5. Now type wvdial. It should connect without a hitch, if your device is working properly. Yes it is that simple.
6. Press CTRL+C to disconnect.
6. Start KPPP.
7. Click Configure to add a Modem.
8. Copy settings from /etc/wvdial.conf for device, and speed.
9. Click Modem commands and add Init2 string from wvdial.conf in Initialization string 1. Paste Init3 string in Initialization string 2.
10. Give the modem a name and press OK to save.
11. Add a new account, and select Manual Setup.
12. Name the connection T-Mobile or whatever you want, and add a number *99#.
13. Leave all other default settings.
14. Press OK to exit the configuration.
15. Type user as Username and pass as Password and connect.
16. It should work.
17. You can enable Dock into Panel in Misc configuration to minimize it into an icon when connected.