Now, at long last, it works.
After a long wait, _Christel_ called Sonera's technical customer service. One hour later, a bloke was here, and 45 minutes after that, we had our wireless connection!
Christel was out when he arrived, but when she came in, he looked a bit apprehensive. I don't know just what she said to Sonera, but apparently it was effective...
I'm in awe of my wife!
