The Motorola C35 to C353 USB is known as the “Motorola USB Device” in the internal ID of the hardware. This was a very popular “Motorola USB Modem” when it came out. The driver for the USB modem has been listed below. Check you hardware to ensure you have a C350 or C353 modem from Motorola.
You will note that in the hardware ID files that it lists the modem by a number of names other than the USB modem that it is. It also lists the modem as a USB CDMA modem and a USB SM6050 modem. as stated above check the modem that you have. Its a small file and an inf file so extract the 3 files inside and right click on the inf file then click install. Very simply to install the driver.
%USBCDMA% = USBCDMA, USB\VID_22B8&PID_0005
%USBPATRIOT% = USBPATRIOT, USB\VID_22B8&PID_1005
%USBLCA% = USBLCA, USB\VID_22B8&PID_3802
%USB1XCDMA% = USB1XCDMA, USB\VID_22B8&PID_2805
%USB1XCDMA5100% = USB1XCDMA5100, USB\VID_22B8&PID_2822
%USBTALON% = USBTALON, USB\VID_22B8&PID_3002
%USBHELEN% = USBHELEN, USB\VID_22B8&PID_4002
%USBNEPTUNELTS% = USBNEPTUNELTS, USB\VID_22B8&PID_4802
%USBEZX% = USBEZX, USB\VID_22B8&PID_6002
%USBNEPTUNEULS% = USBNEPTUNEULS, USB\VID_22B8&PID_5802
%USBNEPTUNELTE% = USBNEPTUNELTE, USB\VID_22B8&PID_4902
%USBNEPTUNELTX% = USBNEPTUNELTX, USB\VID_22B8&PID_4A02
%USBMSM6050% = USBMSM6050, USB\VID_22B8&PID_2A02