Ericsson T28 OS
Ericsson phones since the T28, up until the Sony Ericsson Z600 or so, are based on the same core OS. The main firmware and GDFS files are in .sbn format. Currently, the only tool to deal with .sbn files is wackypack's sbn2bin Python program.
USB PIM/file transfer
Most Ericsson T28-based phones support some form of serial communication. The DCU-11 cable or DSS-25 docking station can be used to interface with the phone's serial connection over USB. Note that the DCU-11 cable cannot be used to modify the flash files of the phone, without being modified.
floAt's Mobile Agent can be used for PIM features and to send files to Ericsson platform phones.