To answer your question as to how complex VoIP is to setup, it depends on what existing components you have within your network and what components within your network you want access to.
If you are looking at getting a VoIP service like Vonage or other VoIP where a router is installed within your network, the order the VoIP router and other routers is specific. In short, the VoIP router MUST BE the first router after your broadband modem. Other routers you use, such as a wireless router, can be installed after the VoIP router. Installing the VoIP router after another router within your network (like a wireless router), will most likely cause problems with your VoIP service. Speaking from experience, to have VoIP using a router within your network, it must be the first router/device after your broadband modem.
Most routers have a web interface; you type something like 192.168.1.1 in the address bar, enter a user name and password, and it brings you to a webpage created by the router itself. The web interface is used to change settings such as security, port forwarding, and more. The same router's also act like a DHCP server where it assigns everything on the network an IP address. VoIP routers, Vonage included, also can act like a DHCP server assigning IP addresses. To add to the confusion, some broadband modems also have a web interface as well as a DHCP server assigning IP addresses. Providing you use default settings on all devices, you will most likely not have any issues with connectivity when connecting the three routers. However, how you connect the ethernet cable to each router, will determine if you can or cannot access the web interface to all devices utilizing such.
It isn't difficult to setup a VoIP service providing the VoIP router is connected after the broadband modem and you use factory defaults for modems and all routers. The difficulty exists in accessing the web interface to other then the last router in line, or port forwarding, or other specific tasks.
I hope this has been a help and not discouraging.
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