My bluetooth keyboard is a device.
My SonyEricsson P900 is a device.
My bluetooth GPS is a device.

I can use them all at once with no problems. I'm not sure why you bolded device in your post - are you saying you can only have one device of each type active at a time? If you start a bluetooth keyboard daemon on the command line, I'm pretty sure you can start up more than one. You can definitely use multiple bluetooth GPS's, and if you use the command line, you can hookup a couple phones and do GPRS from all of them if you want - you'll need your own load balancing setup for that of course.