After your priority date is current, you need to check the processing time of the service center where you case is at. If the current processing time has passed your I-485 RD more than 30 days, then call the service center and talk to a service representative. Tell him/her about it, he/she will send a service request about your case.
Our I-485 RD is 6/25/07. On 7/18/2008, the processing time for NSC was 7/28/2007. Then I made the phone call to the service center at (800) 375 – 5283. Enter your case number and select the option to “report a problem with your case”. Then talk to a representative.
Good luck!