I own an E73 from T-Mobile USA and from the start have had a problem with USB tethering. I have an ticket open with Nokia. It's now going to 3rd level support, but I thought posting here might provide some new ideas.
USB tethering never worked straight from the box with Ubuntu Linux 10.04. After two weeks of troubleshooting, I realized it was necessary to connect it to Ovi Suite or PC Suite first, to "activate" tethering. All the blogs and articles I've read suggest otherwise, but this is definitely how it works here. I "connect a device", detach the cable, reboot the phone, re-attach the cable, and dial once under Windows, and then tethering works for all OS's. Unfortunately, at some future point it randomly dies, and I must go through the whole process again. The rest of the phone continues working normally: the only functionality that fails is the tethering. I have been completely unable to find a reproducible set of actions, but it tends to stop after the phone starts running slowly, after a crash, after a program locks up, etc. For any Linux users, I can run Modem Manager in debug mode and watch it try to initialize the modem. When tethering works, I can see the modem responding. When tethering is playing dead, it is as if the modem is switched off. I've had tethering working for as long as 2 weeks and for as little as a few hours.
As the fix is always a software one, I assume the problem is in the E73 software/firmware. Ovi/PC Suite is changing the state of the phone somehow, and re-enabling tethering. I have been brainstorming ways to spy on the changes in device state, and see exactly what Ovi/PC Suite is doing, but 3rd Edition platform security has been a major hindrance.
Does anyone have suggestions for debugging this problem?? Perhaps a developer tool that dumps the contents of the system folders, OMA settings, etc.? Keep in mind that while I am a programmer, I am not a Symbian developer and the best I could do is write some Python code.
Thanks for any ideas!