This is all very old technology and is available in many...

This is all very old technology and is available in many forms.
Only issue with this is you need to get all of your connections to one place. The Siemens Gigaset series remote base creates a lower cost solution if you do not want to change everything and also removes the need for wires.
If you are requiring an end to end solution and using Engin broadband and VoIP it may be a suitable solution but nothing really new, its just another product.