Running in 4G/LTE and being a big "latch on" user of Wi-Fi as I wander around Europe, and for the next while, Lisbon has me staying in touch more and more by voice vs. email and text messaging with friends far and wide. Depending on the person, some still use their mobile number, but more and more of my travel buddies, those other nomadic types I know from Australia and the UK are far more reachable using other means.
For starters I'm finding some like Viber while others like WhatsApp. Still others are massive users of FaceTime, and a few holdouts are still on Skype and the uber-geeky crowd is on Wire. But what is common to all the services being used is one thing that separates them all from the mobile phone. Each and every call is in glorious HD quality voice. When I'm on with someone on Viber or WhatsApp it's like a T-Mobile to T-Mobile call back home. Clear, crisp, rich and robust audio.
The more I use HD, the less I like regular calls, but alas until the entire telco world goes HD, thankfully we have those alternatives available to us.