Frequently here in ATL on Clearance Delivery, I will have a SKW ask for his/her clearance with the 4-character calls ign (i.e. SKW4001). The first thing I do when I dont see that # in the bay is ask where they're going and look for some shortened version (i.e. Like a SKW40B) going the same place. I then usually say "I don't have a SKW4001, but I do have a SKW40B going to XXX, could that be you?" We work it out on CD, which is the point I was trying to make at the start of this thread.....if you have an "A" now appended to the end of your call sign (one that already had a 4-character number), check with clearance delivery (this is the BEST time) and verify what call exists on your flight progress strip....then use that call sign for the entire flight segment when it comes to ATC communications.