the real SR's never filed a plan...only mission ops did it but they certainly didn't mention it was a SR-71. most of the time, they filed a plan with a KC-135Q.
above 60 000ft it was absolute silence. if there was some aicraft in the neighbourhood, it was another SR or a U-2, but they held contact with each other.
this is the book i meant:
http://www.habu.org/graham/sr71revealed.htmli have both his books, but the first one is much better. it describes in every detail how the cockpit looked like, how you had to control the engines, how a mission went by,... a must for every Blackbird fan!!!