Same story here. My bill is due today and that number rang me this afternoon. This isn't the first time though. My call logs show they also called last January 12th, and before that last year on August 3rd 2010. In august apparently I actually stayed on the line with them for 51 seconds.
Maybe it's not a scam or maybe it is. All I know is that I live in an 818 area code and it seems there is something odd about the phone system they're using. I'm theorizing it may be an automated switchboard that dials a data list of customer numbers while some poor underpaid Gas Company employee just sits there waiting for the call to be connected. My guess is that they get so many non-pickups, voice-mails, and busy signals that most of them have fallen asleep by the time a customer actually answers.