You can use 4 types of phone with the Vaya IP40x series
Digital - connects to the unit directly and powered by the unit
Analogue - connects to the unit, limited functionality on the handset
IP Phone - connects via the LAN can be POE or powered by 240v
All 3 can use the Phone Manager software to control the phones. You can use an analogue handset but by using the phone manager software you can use the full functionality.
Soft Phone - use a latop as a phone controlled with the 'soft console' which is identical to the phone manager software.
You can use the IP Phones at remote sites with have a VPN. If you have Phone Manager 4.01 or later software, some handsets can set up their own VPN and connect to the system.