For those who don't know, you can create a Google account on an old phone, then download and install the following two apps, make some setting changes, do some verifications and in most cases turn that phone into a completely free phone for both incoming and outgoing voice calls, texting AND video calling using WIFI through VOIP from most parts of the world, and (according to Google), to any phone in the world. In other words, this is something you don't need to buy minutes for in most cases (with a few exceptions in certain parts of the world where calls are charged), again all without a real cell phone account or calling plan on the phone.
Google Voice: Use to obtain a Google Voice phone number. It requires a little trickery, in that you need a real cell phone number to receive the verification text and activate it. I was able to do this by first adding the new Google account to my active Droid Turbo 2 cell phone, thereby linking the new Google account to my existing one. Then I removed the SIM card from the Turbo and installed it into the second phone, a MOTO X, and then added the Google Voice account on that phone to get the Google Voice number.
In order to activate the Google Voice account, it asks for permission on the old phone (in my case the Moto X), and texts to the cell phone number active on the phone (the reason for the SIM card temporarily), to verify the account. Once it's verified you can remove the SIM card, and the Google account and Google Voice phone number remain active on the old phone. Aftewards, I removed that new account from my Turbo and it remained active on the Moto X.
Hangouts Dialer: Use to make VOIP phone calls and texts completely free Hangouts Dialer will use the Google Voice number to make and receive calls and as long as it has internet access (WIFI), the phone will both make calls and texts (and even video calls), out of the gate completely free, but it won't receive calls or texts yet...
In order to get the full functionality, open the Hangouts Dialer, then tap on the menu of the call log list (top left, three underlines). Then select "settings" where you will be taken to the settings screen. Note: If there is more than one Google account on the phone you'll be taken to a list of active Google accounts. If so, simply select the desired gmail account with the Google Voice number associated...then in both cases, you'll see the list of setting options. Scroll towards the middle of the settings list (bottom of the first screen or just below), to where it shows "Incoming phone calls", and make sure to change the selection on the right to on (Green). You may also want to turn on "Messages" right below to use text messaging to the fullest.
To prove it works with both phones having been verified from the same SIM card and phone number, I made calls between the two phones and they both went through. Then I made a call to another phone and it also went through. Next, I did texting back and forth and in all cases they worked like a charm.
