Slightly off topic, but I can confirm that the 2820 works very well with a 21CN BT line. The previous router, a Cisco 877 would drop connection several times a day and managed to confuse the BT DLM system into increasing the target SNR unnecessarily high to 12dB.

The Cisco synced up at around 11 to 13 megs, the Vigor 2820 syncs much higher at nearly 16 and has been rock solid. I am expecting even higher sync rates when and if the BT system reduces the target SNR (usually after a few weeks of stable operating if you're lucky).

Also, interestingly the Vigor 2820 supports SRA (Seamless Rate Adaptation), a feature of ADSL2 that allows the sync rate to vary in the face of varying noise and keep the SNR relatively constant and this appears to be operating on my Vigor and 21CN line.