KPN still has POTS lines. Mostly in use by elderly people, alarmsystems en, indeed, elevators.
They are delivered without internet. The central infrastructure for POTS works with VoIP connections; at the cliënt home it is a pure POTS line.

If the cliënt also want internet then it’s VoIP. But… via de RJ11-connections for phone on the modem it is analog, so equal to POTS.

KPN has real VoIP only for businesses.

But within a very short period of time real VoIP will be available for consumers as well.

With a VoIP ATA like the Grandstream HT801 you can connect a normal oldfashioned telefphone to your VoIP subscription.

Hi Peter, thanks for coming back to me, I am specifically looking at Data Centres here, usually Data Centres would have copper POTS lines to the outside world for Red Care and Life Safety such as a line to an emergency service such as the fire brigade. What I am looking for is in the Netherlands they are changing this system from analogue copper POTS to using fibre VoIP instead, I am looking at how this would be presented within a Data Centre.

I think it would be better if you ask that question on the KPN forum for businesses.

In general you can say that the alternative is to use a VoIP ATA. This enables you to connect a "normal" analoge telephone to a VoIP subscription. That's it, nothing more.

Now ofcourse there is more to it as with VoIP telephony wil use the Internet infrastructure instead of the copper POTS lines. This makes you a little bit more vulnerable as when Internet fails your telephony will fail as well. This is why there are a lot of organisations that will use 3/4g as a backup in such situations.