TextPlus which with a free download gives you an add supported number for text messages in the area code of your choosing (Canada and U.S). The app also offers really affordable minutes for making and receiving voice calls with the number, and despite a bit of lag the voice calls are fairly dependable over wifi.
On top of that, I've got Skype, iMessage, Facebook Messenger, and FaceTime all of which let me supplement phone use over IP. I use a mobile hotspot to keep my laptop connected when no wifi is available, and I still keep my phone charged at home to make sure I'm not missing any calls at my old number, (though most of my friends, co-workers and clients have gotten used to my TextPlus number). Though a tablet might seem like a less than perfect solution to making a call (since you don't really want to hold a tablet like a phone), the addition of a Bluetooth device makes the process a bit more elegant. I've even considered maybe picking up the new iPod Touch to supplement my need for a more portable device and camera (at $299 it's cheaper than an early upgrade) but so far using my other devices (which are always with me anyway) have mostly filled the gap left by my phone. More and more I wonder if I even really need a phone. With all these connected devices, and ways around relying on cellphone coverage I've gotten by without too much trouble. I've even costed out the difference, and technically between my hotspot and the minutes I bought with TextPlus, I'm still spending less than I am on my phone. There are a few caveats (portability is a big one), and of course the convenience of a smart phone can't be denied, but generally living with a "phone" hasn't been nearly as frustrating as carrying around a phone on it's last leg. (Images: Sean Rioux)