rilgsm.dll is the device driver for the RIL1: device. On Blueangel rilgsm.dll opens COM2: and COM9: which are handled by serial2.dll and serial3.dll
the RIL_ functions are in ril.dll, which opens RIL1: and uses DeviceIoControl to communicate to the device.
rough overview of the relation ril-functions - rilgsm ioctl - gsm at command