I've just found a way for MacBook OS X to recognize my SonyEricsson M600i as USB Flash Drive.
Maybe because there are a lot of users of M600i who also use Mac OS X, so we have to try solution and help each other since no official driver available to download, neither from Apple nor SonyEricsson. One thing is to have the phone as GPRS/3G modem dial-up, this was solved several weeks ago. Now this USB mount drive has been solved. Hope in the next release (Leopard) iSync can detect my phone.
Back to the topic, here is the procedure to have your M600i act as USB
1. Download kext file from Magnus Blog. (M600USBFileEnabler.zip)
2. Extract the file to anywhere
3. Close all running applications (this is a must since you have to restart computer later)
4. Run the installation file extracted from zip
5. Follow the step in the installer (basically you just hit the next button)
6. Upon completion, it will ask you to restart computer.
7. After restarting, change your M600i USB setting from "Phone Mode" to "File Transfer"
8. Plug data cable from phone to computer
9. Pray that your Mac will detect a new storage and mount it. (it works for me!)
FYI, I'm using Mac OS X Tiger 10.4.9 and SonyEricsson M600i (firmware R4C01). Lower version of Mac OS X and lower firmware should be working to according to the site. Great work for Magnus, bravo!
Latest Update : As I'm using Mac OS X Leopard 10.5.3 right now dan my M600i Phone firmware is R9F011, it seems that without installing plug-in above OS X can automatically detect the phone as USB Device.