Simple, yet a bit too convoluted for most people. iPad Mini (Verizon LTE) + Google Voice + VOIP phoning app (Talkatone). Double bonus because I have bad eyesight and iPhone screen is too small for me. Sans all the jokes about carrying it around...I leave it in the car often. Or, Bluetooth/WiFi the free personal hotspot to my old iphone 4. Mini is wrapped in an Otterbox Defender and sometimes just carry it around like a small book. Fits in the pocket of most of my cargo shorts/pants... Not doing much conventional phoning, anyway. Done. For $20 bones a month.