When I owned a BB 9530 storm I looked around for a RPN calculator to use. Found what I was looking for in app created by a Doug Braun who had ported a java version of the HP25, created by Lawrence Leinnweber, Cleveland, Ohio USA. I used this for the 3 years that I had my 9530 and it works great. I have just moved to the BB Torch 9850 and wanted RPM calculator back.
So I did another search and found an update on Doug's work at hp25c sourceforge.net, created by Bruce Reidenbach This one is nice in that he replaced the screen shot of the HP25 with a custom bit mapped image and added alot of enhancements to programming and stack registers but did not publish the source code. So, I took the source code from Doug's work and added in the new and resized and tweaked bit mapped image and remapped the buttons to the 9850 screen size. I left a message on sourceforge to see if Bruce would share his code enhancements so that i could incorporate into the Torch 9850/9860 version but I have not heard back.
Anyway here is hp25alx.zip file that you can use RIM's desktop manager to load onto your Torch.
Here is OTA link to load directly to your phone HP25.jad
Screen shots from the simulator, it works on my phone also :-)
Menu
Realistic
Draw
landscape
Picture of real HP25 calculator