The 888 number I cited was what was provided to me within the paperwork I received when my OPM DR case was first approved in 2008. Upon calling that number I was given another (202) number to call, which was to a wrong case worker. After numerous calls and transfers (about 8) I was finally given the number I call now. This number is for my District and Service Group. The number I currently call is (202)606-4289, however as I stated previously, this number is seldom answered directly and if a message is left, no one responds.
I think it is interesting that so many of the people handling the DR cases seem to take extended sick-leave. I was given this same excuse for two different workers that were supposedly handling my case, only to finally be told that my files had been "lost".
The number you show for Retirement Services is in Boyers, PA and they do not handle Disability Retirement. They will tell you to call the (202) number. I find that calling any (202) number is a ridiculous situation, as the caller has to pay to make this call, and since those calling are disabled and trying to get money to live on, having to pay for the call, especially when it has to be done over and over and over, is an unnecessary hardship.