ProJazz.net

“Pennsylvania 6-5000”  is a 1940 swing jazz and pop standard with music by Jerry Gray and lyrics by Carl Sigman.  It was recorded by Glenn Miller and His Orchestra as an RCA Victor Bluebird 78 rpm single. According to a TV-interview with John Best, he originally improvised the famous trumpet-solo on the Glenn Miller recording of PEnnsylvania 6-5000, and it is widely emulated ever since, on that tune (Wikipedia).