 active number, they call it a CSA number, because without that number, you're not going to get to talk to anybody. If you're in that limbo stage where you've just left the agency, call back to your HR office. They can probably help you with any questions you have until OPM takes over. But if you are going to call OPM as a retiree, I suggest by all means call early. If you're on the East Coast, it's a little easier because 7.40 a.m. is 7.40 a.m. The earlier, the better.