MacOS X provides a kernel extension that can talk to the modem
interface on phones connected via a direct USB cable. This kernel
extension is named USBAppleCDCMDriver.kext and will be
autodetected and used if the chipset in the phone is supported. This
will create a device entry called usbserialXXX. The
XXX will vary based on how the phone is plugged into the USB bus.
This can be used in the System Preferences panel as a network interface
for PPP connections provided you have the correct modem scripts.
MacOS X does not provide device drivers for USB to serial converters. Since there is a wide variety of converter chips, there is also a wide variety of drivers that you will have to find on the web. (Often the chip manufacturers do not provide them, but their OEMs do).
BitPim can access USB devices directly. Note that you must not have any program or device driver using the data interface. It is OK to have the system kernel extension loaded providing access to the modem interface at the same time you use bitpim to talk to the data interface.
BitPim Online Help built 17 January 2010