Ian Richardson presented the following explanation :[color=blue]
> I'm looking to replace our NTL telephone service with a VOIP one using the
> NTL broadband connection I've got.
>
> I guess I could use an analogue telephone adapter (ATA), and use my existing
> PSTN-based DECT answerphone.[/color]

Yep.

[color=blue]
> I'm using a Linksys WRT54G router flashed with SIP@Home-enabled DD-WRT (so I
> could then use a SIP-enabled wifi phone for around the house), but as the
> cost of a standalone ATA appears to be about as much as a replacement
> wireless router with built-in ATA, I'm also up for any suggestions on
> replacing the router (as long as I can also flash it with DD-WRT).[/color]

Look on Broadbandstuff for the Linksys/Sipura SPA1001 - very good ATA.
I use the same router as you with NO one-way audio issues, or port
forwarding requirements. Don't bin it. You could get 3 or 4 SPA1001s
for the price of a WiFi phone - they're also not the most reliable of
devices, by all accounts.
[color=blue]
> The only pain is that I also have a Sky HD box connected to the existing
> phone line.[/color]

Disconnect it. No need to have it connected & it won't dial in using
Voip - the modem within the Sky box will only connect at speeds above
those which can be (relatively) reliably achieved over VoIP.
[color=blue]
> Rather than replace the existing wired extension with an
> alternative, it looks like I could use a wireless phone extender
> (specifically the one advertised on[/color]

For your Sky box? Don't bother.
[color=blue]
> [url]http://www.netshop.co.uk/productcategorydetail.aspx?categoryid=55456[/url], as
> most sites claim that alternatives don't work with Sky+ or SkyHD boxes).
> Unless, of course, anyone knows differently.
>
> Oh, and is there a way of doing this such that my existing NTL telephone
> number could be used with the VOIP provider?[/color]

No. Unless it's a BT number that you've ported to ex-NTL.