Poll

Even if I didn't have any phone service, I'd still carry around a cheap old phone (at least in the car) to take photos, get driving-directions/find stores, read email and RSS feeds (updating when near WiFi), play games, be able to call 911, give search&rescue a signal to follow, etc.

But I really can't see opting-out of having phone service these days, as there are several available for FREE, and very cheap, today.

If you've got just any licensed Android 4+ device, you can install the Hangouts Dialer to make and receive calls via your Google Voice number (via WiFi). Even without an Android device, you could still get a Google Voice #, and check your voicemail messages online.

If you have a Sprint/Boost/Virgin phone*, you can bring it to RingPlus and get 125 minutes/40sms/10MB without even giving your credit card#. They play music & ads (instead of just ringing back). and of course hope you'll want to upgrade to a paid service (starting at $2) later. NOTE: Verify phone compatibility right away, and quickly return/exchange any used phone that fails activation checks.

--Less Recomended--
FreedomPop also offers BYOD on Sprint & offers 200minutes/500sms/500MB if you don't mind paying $20 in activation fees, a few dollars for voicemail, and constantly trying to trick you into buying extra services.

You can buy an Ooma Telo VoIP device for ~$100 and get mostly-unlimited free VoIP calling if you're careful to opt-out of extra services, and already have a good internet service.

I hated the old days, when phone service I only barely used was $30+/month, plus some minimum monthly fee for long-distance I almost never used, and that on-top of monthly (slow) internet service subscription, while being inundated with sneaky telemarketers and worse.

* http://www.prepaidphonenews.com/2015/02/sprints-blacklist-is-gone-but-byosp-is.html