RDM+ is its own solution requiring you install client software on every PC you want to connect to.
However, Idokorro Mobile Desktop (terrible name), is a true Remote Desktop application for the BlackBerry. I've tried both, and was able to make IMD work with my BES connection, but was unable to make it work on my BIS or TCP connection. Idokorro Mobile Desktop
I can tell you that in terms of convenience, IMD is awsome. It supports RDP and VNC protocols. And if using RDP, lets you set the client resolution in advance (320 x240 or 640 x 480 work great). I also find the mouse clicking action much easier/practical with IMD than RDM+.