I'm assuming thats NetworkManager. If I remember correctly, for 3G connections, it creates a profile that will be used with 3G dongle/phone. In that profile, you can set the signals to use. Either auto, UMTS, or GPRS. Changing this to UMTS forces the connection to use only 3G signals.i dont use specified application these days using ubuntu with default network application

man pennuwe application eka