Thanks for the notice.
I just updated my 2011 F10, build date 10/10, and it left my MX at 2.5.21, but upgraded my TX from 2.5.21 to 2.6.4.
No changes or improvements that I have noticed.
I am disappointed to say the least, as I was hoping both Telephone and Multimedia versions would be upgraded to verison 3.5.4.
I believe based on my build date, my Combox is P/N 84109244191. I am guessing version MX/TX 3.5.4 is only for the newer Combox versions, P/N 84109251739 or P/N 84109257153.