Finally, after weeks of intermittent internet access, the problem seems to be resolved. Last week, between Gumby and I and AT&T, the modem was agreed to be replaced after talking to four AT&T representatives. First was tech support. Then account services. Then tech support again, I think, different person. Then manager because they said the modem is out of warranty and cannot be replaced at no charge. Manager asked for the serial number of the modem and then determined that the modem serial number is among those determined defective. Manager took care of the approval and transferred us to the equipment replacement department. That was Friday. Now Tuesday, the modem is here. All is hunky-dory. Mucho gracias, AT&T. I think it would have been resolved earlier, except the other time that we attempted, the equipment replacement department wasn't open (it was a weekend).