I have had BT Broadband with BT Voyager100, since January, I had quite a few problems with intermittant dropouts (being disconnected while on line).
It was suggested that it was the viatech chip, but this was not the case, BT were excellent, re-running cable from the telegraph pole to the house, and then to my modem. then replacing the modem.
After three visits by their engineers (all free of charge) it was found that the problem was caused by old internal telephone wire (30+years)
totally unrelated to the line to the PC modem.
after disconnecting this cable and buying a cordless phone, the Broadband is excellent.
I can't praise BT enough for their after sales service.