I had many of the same problems others have reported here connecting my Nokia 3650 to my PC using a Belkin USB/Bluetooth adapter (F8T001). But I kept playing around with it, and mRouter, and then noticed that, hello, the icon for mRouter had changed. What's this? mRouter reports it connected! Then I started up PC Suite and it works like a charm... Just backed up my phone, sync'd my contacts and calender, no problem...
So the Belkin USB adapter *can* work.
As to getting it to work, here's what I did
1) I went to the Belkin site and downloaded the latest driver (F8T001.exe). My version is 17,659,904 bytes in length.
2) Go to mRouter (in the system tray) and tell it which COM ports to use. Check the ports you chose under "Local settings" and "Client applications" in your Bluetooth configuration.
3) Start the "Bluetooth serial port" service under My Bluetooth Places\My Device (right-click, choose start).
4) Double-click "Bluetooth serial port" under "My Bluetooth places\Entire Bluetooth Neighborhood\Nokia3650". You will get a message saying "The remote device closed the connection" BUT if you look at "Bluetooth serial port" in My Device you will see the Nokia phone listed there. And the system tray icon for mRouter will change to show the connection is working.
I may be leaving out some important step here--I spent hours playing around with this until it finally worked. But the point is, it can work.