I'm using this on a VDSL line after a summer lightning strike on a nearby tree fried my router (and a few others on the street). As expected the sync speed has dropped from 30Mbit/s to 28Mbits downstream and 5.8 to 5.5 upstream and curiously the standard phone now rings continuously on a incoming call - the DECT phone is quite happy with whatever effect is happening.
Given that I never sustain maximum data transfer rates this is not an issue, especially if it means the next time we have a storm I don't end up having to spend £200 on another Vigor - thankfully in the six months since I've had it we've not had a real live "what the eff was that" situation.

















