I use Nokia 3100. I've read the emails in this board and it seem my problem maybe related to the cable itself which might not be a true Nokia's DKU-5 cable. The USB to serial chip might not compatible with the Nokia driver?
Okay, for everyone with a generic DKU-5, listen up!
I saved myself a lot of grief by using the drivers from the following page. Was even able to get the nokia software to synch on first try!!! (you do need to tell the connection manager which port it's on).
Step 1: Extract the driver file <http://www.ringtonerfest.com/usbcable.zip> into your hardisk of computer
Step 2: Connect the DKU-5 USB data cable to USB port of your computer
Step 3: The computer system should detect there is a USB device found, then select the corresponding driver of operation system for this USB data cable, then the computer system will assign a virtual COM port (COM port 3 or COM port 4) for this USB data cable. (you may also find the corresponding number of virtual COM port which assigned for by system in hardware secection of system in contral panel).
Step 4: Install the Nokia PC Suite software, during installation, the software will try to detect the USB data cable, you may just waive it, and select COM port 3 or COM port 4 which assigned by computer system to go ahead the PC Suite software installation.
Step 5: After the Nokia PC Suite software successful installed in your computer, then re-start the computer.
Step 6: After the computer re-started, power on the 7210 mobile phone, then connect the 7210 phone to the computer via using the DKU-5 data cable.
Step 7: You may see the 7210 phone under data mode, and the Nokia PC suite should detect the 7210 phone found, then you may run PC suite programs.
Problem was finding the correct driver. Instead of an entire evening or more with this, our friend google saved the day!
I haven't tested this as a modem, but I doubt I will ever want to use it for this. I have a nokia desk stand/port that I was using to power and just wanted to be able to synchronize without using infrared. Time to upload some tones and wallpaper!