Thanks for your answer. I tried those switch messages and I can confirm they work. Using your help I can now switch to broadband modem mode! :) So, on my E303h-1, - 12d1:1f01 is the default (mass storage device) mode - I can switch to 12d1:14dc ("ethernet" mode) using either 55534243123456...

I don't think it makes a difference. Different versions of the Huawei E303 seem to use different product IDs for the ethernet and fallback modes. Specifically, I had a E303s-2 (HW version CH2E303SM) and now I have a E303h-1 (HW version CH1E3531SM). (You can see your exact model id inside the stick a...