I can't seem to get this? I had a Google Voice number a long time ago, and it lapsed so I can't seem to get it back. It looks like I'd have to pay to use Hangouts to call anyone, too.
Instead, I pay for localphone (a few pence really) for a US local number and list that for a contact for those companies in the US that still need a local number (banks/credit cards/etc). It will forward calls made to that phone number to my UK mobile phone and charge me a really low rate (no one has called me yet, but I only put it in place in case banks need to call me/etc). I also paid for Skype world or something so I could call my friends and family back home as much as I want.
If I could get hangouts to work and it's cheaper than Skype, I'd consider that!