ZTE USB Modem not working in Yosemite

I found a solution from web and it works on my ZTE-MF667 with no problem.

1. Go to System Preferences → Network

2. If you see your USB connection on the left side go to step 5.
   If not, select the "+" icon like this.

   

3. Select your Interface and set your Service Name like this, then select Create:

   

4. Select ZTEUSBModem and set Configuration-Default, Telephone Number: #99*

   Account Name and Password must be blank.Then select Advanced

   

5. Set Vendor: Generic and Model: GPRS(GSM/3G)

   

6. Click OK and Connect.

I suspect that your problem is a USB device problem. For some reason Yosemite is not creating the proper device file entry in /dev when a number of USB devices are plugged into the system. Because there is no /dev/ entry after plugin, the software is not able to access the device.