Or you could do exactly the same thing from your Android phone, provided you've rooted it. Installing Cyanogenmod makes it even easier (you won't need to download an app; the wifi access point is right in the settings), but isn't required.
I'm curious, what kind of data transfer rate do you need to get a solid call through? In the past when I tried to make WIFI calls through Google Voice "Hangout Dialer" the call quality was poor.
For VOIP calls you don't need much bandwidth, but you do need low latency and low jitter. Both are pretty bad on cell-phone data connections, so it's rarely worth the bother.
However, these comments are about providing a wifi hotspot that routes over the data connection rather than VOIP.
