Hi Brdleis and welcome,
Fengtao split off the Mobile app some time ago and now each app has its own respective purchase price. So for the trial, you will need to download the Mobile app as well...at least this is my understanding. I purchased back in '04 and last year when Mobile was released, it came along with Platinum as a freebie.
Anyway, once you download the Mobile app, they'll be appropriately married so as you open Platinum, the Mobile features will appear as well.
Hope this makes sense and hope it helps.