Just received this VoIP ATA (Analog Telephone Adapter) from Amazon and just got it setup for Google Voice.
Amazing, works great and I can make calls from a normal telephone (corded or cordless).
The device is called OBi100 VoIP ATA & Voice Service Bridge by Obihai Technology, Inc.
They also make another model OBi110, this model provides an additional connection for your landline (if you have one for your current home phone).
I'll have a picture of it on the setup, it's simple and cheap.
I considered using the Cisco SPA Voice Gateway, but the cost is higher and I didn't really like the reviews on it.
The folks that makes the OBitalk devices were from a company (Sipura) that Cisco bought over that makes the original Cisco SPA hardware.
So you'll need an internet connect (everyone has this...), a normal corded or cordless phone, a spare ethernet port on your router/switch, and a power socket for the OBitalk device.
Of course you should have Google Voice, if not, you'll have to set this up, btw, you'll need a telephone number, that Google Voice requires for call forwarding, I use my cell number.
Some information about ATA click here - Analog Telephone Adapter.
Oh yes, you know what's great?! It provides an app on your Android or iPhone that allows you to call your OBitalk device via wifi or mobile broadband, so if you're in a hotel or a place that provides free wifi, you can call your OBitalk device. OBihai provides a device number like a phone number that you can call.
Update... you can watch a video of it... Here