I noticed that USSD codes (i.e codes checking for balance etc, eg: *123#) are not well supported on our Lumia. Sometimes it really takes ages to process and display the response, and many times it would just hang on 'waiting…' screen and finally you have to dismiss it and try again.
Again the response oriented USSD codes doesn't support at all. As in my Telecel prepaid, on dialing on *140# I get a response screen with selection. If it sometimes displays me the option menu, there is no space given to input my selected option.