Yes if you are using a Desk Phone that plugs straight into an ethernet port either on a router or via a switch.  

However please note that your broadband will need to be of sufficient quality and bandwidth in order to support having multiple VoIP lines and the use of the web.  

Some businesses use a two separate broadband lines one dedicated for VoIP, the other for the internet so you may need to speak with your current broadband provider about this. 

No, if you are using Dect Phones with Base Unit(s) as it is is the phone equipment that determines the line capacity NOT adding in extra phone lines or extensions.

When using the cordless Gigaset Dect Phones which are connected to a Gigaset Base Station plugged into a router, then please be aware that there are limitations with the call capacity which is a base issue as depending on the model of base used you may have up to 4 consecutive lines in use per base so if you require more than this you may need to purchase an additional base station, please click here for more information.