I'm traveling internationally soon and will have unlimited internet usage but regular calling/texting will be restricted or I'll have high roaming charges. So I'm wondering how Google Voice works... is it like a relay where someone calls my Google Voice number and and then Google calls my regular number to complete the call? Or is it pure voip and will work through internet service alone? And will call quality suffer/improve depending on internet quality/speed? Thanks in advance
A Google Voice number forwards any calls it gets (and I believe texts) to numbers you set up. There is an option where all calls to that number can also ring in Google Hangouts.
If you are travelling, you could download Hangouts on your phone and make a temporary Google Voice number forwarding calls to your home phone. When the number gets a call it will ring your home phone and in your Hangouts app if your phone has access to internet.
If you choose to answer it in Hangouts, it's the same as having an internet call with the person who called you. Call quality will suffer/improve depending on internet quality/speed.
If you are going out of US/Canada, I don't know if you will be charged for calls. Most questions can be answered here