I see where you're coming from now....
Yes, the purple blob (probably the best way to descibe it

), is a VTA (or IPA to some people), and will allow you to plug a normal landline phone, into the VTA, and make calls using the Tesco internet phone service.
The Siemens one is a really good price (currently �50) and is an internet phone, but one that plugs into your router, instead of the USB port on your PC (like the other "Dualphones").
Both of the above, as they connect to your router (rather than a USB port), will work independently of your PC (so the PC can be switched off, whilst leaving the phone working).
The only problem I'd have with either device (but my gut feeling would be to go for the Siemens one), is whether they are locked to the Tesco Internet phone system (i.e. not able to be used with other VOIP / SIP providers).
From what I can find (on the Siemens DP450), it appears to be a Tesco special, but works in two modes - DECT and VOIP.
This could (but information is sparse) mean the Siemens phone can connect to the Tesco Internet phone service (the VOIP bit) - appears to come with a black box (presumably the link between the phone and the router) - and to a regular DECT system (if you have one connected to your landline).
The other way of reading this, is it uses DECT to communicate with the black box (and thus, to the internet).
All of the other Tesco "Dualphones" are USB only.
There is, of course, no reason to stick with Tesco phones, unless you wanted to stick with their internet phone account.
There are plenty of other choices of VOIP provider, although I'd not recommend Vonage, because of the high price of changing products, numbers, additional services, and the charge you around �20 to leave!
The advantage of the Tesco stuff, is you do get 59 clubcard points
Ade
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