Was the Voyager supplied by BT in conjunction with a broadband package? If so, it may be "locked" to their service by accepting only a valid BT login (email address?). Retail versions of the router obviously wouldn't have this restriction.
I understood that the Netgear DG834 router supplied by Sky was "customised" for use with their service, which might mean that conventional routers won't work.
The Sky router is a Netgear DG834GT but Sky have customised the firmware and you can't access certain features that you can with any other retail DG834GT. AFAIK this includes obtaining the username and password. The utility I linked to can get allow you to access certain features that otherwise would be inaccessible.
Other Sky users have successfully managed to connect with different hardware after obtaining their details as above however if you do this you are in breach of their t & c's.
The modem could well be locked but I didn't think it was compatible with faster broadband connections anyway, according to BT.