The situation is as follows:
- We have a Nokia 6120 classic mobile phone with USB cable (special one, for Nokia 6120 classic)
- We have a PC with a modern Linux (Linux Mint 11 in my case)
- We want to transfer files between the phone and the computer
The solutions is to:
- Install obexfs package (I used Synaptic Package Manager from Linux Mint)
- Create folder for mounting mobile phone file system – lets say it is /media/nokia6120
- Connect the phone to the computer by USB cable
- Login as a root (or use su command)
- Invoke a command:
obexfs -u 1 /media/nokia6120/
That’s all! 🙂
The Art of Code 
UPDATE: this is not needed with latest Linux Mint 14. When pluging Nokia E52 by USB cable to the computer the phone memory gets visible in file manager (Nautilus or Thunar) so file operations are available.
UPDATE 2: it turns out that Nokia 6120 classic is not cooperating as easily with Linux (latest Linux Mint) as Nokia E52. So obexfs is somehow still needed for Nokia 6120 classic. Here is some very interesting article about this:
http://www.smokinglinux.com/tutorials/nokia-pc-suite-for-linux-with-obextool-on-ubuntu-gutsy