- is it possible to install a UMTS card with that units only with "installing" the right PCIe card or do they need any additionally work (antenna, SIM card slot)?
Yes, just go with the card recommend on the Wiki, those are certified to work with OSX on D models atleast (i havent tested on any of the models you are look at)
- does anyone tried or can be helpful with an 8GByte RAM upgrade (any kind of experience with this)?
More memory is allways good
- what exactly does the BIOS mod work for:
It adds modifications to your bios needed to run OSX, while its not required because those can be applied using dsdt.aml in /Extra
:- is it "only" for a hassle free kind of installation?
Yes
:- is it working transparent (like EFI-X) or does it need any kind of boot procedure?
Dont know, havent tested EFI-X
:- is it covering any kind of OS upgrade problems?
No
- is the BIOS mod working for the M6300 too?
No
- could not find any information about the M4400, does there exist any user with experience on it?
that model is not covered by us .. yet..
- I like the heavy and alu design of the M6300 and would like to get known, if it will be the same with the M4300?
No idea mate
- any experience about battery usage under MacOS X Lion are welcome
Dont know what to say here.. seems the same as under SL.. depends offcourse how you use the machine.. but thats common for any OS