While we are on the subject of call letters, it's worth mentioning the best call letter origin site on the web, http://nelson.oldradio.com/origins.html There are over 3500 call origins listed there! Bob Nelson does a wonderful job of maintaining the list.
So, that would indicate that there are 17,576 (26x26x26) possibilities each for calls beginning with K and W. From KAAA to KZZZ, and WAAA to WZZZ, of course minus the inappropriates, like KSEX and WSHT.
And this is after three letter calls, like WLS