If the calls you make are outbound (you calling others), I suspect the iPad Mini + VOIP app will work great for your situation. You may even find that you have wifi enough that you don't even need LTE/3G for periods of time, which will save you a lot of money vs. a 2-year contract obligation whether you use any LTE/3G or not. VOIP-based inbound calls are a little shakier, though some VOIP apps are better than others for this.
If you are worried about the phone-side backup, some are suggesting an iPad mini + a cheap "dumb" phone with cheap plan... but that does yield 2 devices to carry around instead of one.
Myself? I'm thinking iPad Mini with LTE + VOIP. Like you, I don't need much phone capability and I already know VOIP will cover what I do need. I also have wifi in most places, so I'll use the LTE side of the mini only in situations where I really need to connect right now and can't locate any available wifi nearby. I rarely need to receive inbound calls (odds are high that such calls will go to voice mail most of the time), so I'm mostly calling people back. VOIP with just data is perfect for that.
Some people- usually those who already own iPhones- have a very hard time seeing this as a potential iPhone replacement. But for those who don't really use the phone portion itself, I could see this being a great option. Even if you need LTE/3G connection all of the time, the plans are much better than the iPhone LTE/3G plans. Earbuds + microphone for calls, everything else is apps on a bigger screen.
Thanks, and you are confirming some of the points that I am considering.
Plus, with Facetime capability... the new iPads should already have microphones built in... although earpods or the like may work a bit better.
Really the two issues that are not very common, but might be a bit tricky in a pinch, is receiving incoming calls or being notified of voice messages, and 911 access in an emergency situation.
I have thought about migrating my iPhone 4 to basically be an iPod Touch plus Pay-as-you-go phone backup. I could replace the screen if I knew I was going to keep it a while longer, or get a solid but "dumb" burner as a replacement to stash in the car or go-bag.
The iPhone 5 is fancy, no doubt, as a smart phone. I am just not sure that I would use it's advantages, for the money and contract committment-re-up that it would cost.
The big thing swaying toward iPhone 5 or iPad 4 is the A6 chipset, and the big increase in system speed. It may be a big boon now, but it also is a benefit for the longevity of the device for future software.
An iPad Mini with that performance boost would be welcomed, no doubt... but that doesn't necessarily make the A5-equipped iPad Mini a bad device as some of the commentary around here suggests.
The screen resolution doesn't bother me so much, but it is one of the things I am waiting to see first hand. iPad 2 looks quite good... and that resolution shrunk to ~7.8 inches is only more pixel-dense.... even if it isn't "retina".
I probably have more concern with keeping my glasses clean enough to see that precisely, than I would with the difference in resolution.
Part of the issue with iPhone for reading and info presentation is that things are so small that you have to look closely.
If the text and such were really small on the iPad Mini, you'd have to hold it closely also... and at 20-30 inches away (bent arm's length from face) from one's eyes (rather than having to hold it actively closer at 6-10 inches from face), I doubt there will be night&day difference for iPad Mini vs if it were "retina" and scaled to be text-legible. Again, welcomed if it were there... not a deal breaker for me not to be there.
And if 330$ base price is a deal breaker on price for some... A6 and Retina display would probably inched the price up a bit further, and garnered more criticism than it is now getting. Then there is the whole "fratricide" argument about competition with the iPad 4 with nearly similar prices and specs, and mini having a size quantity disadvantage, while iPhone 5's subsidized entry price would be notably lower also.
iPad Mini is in a somewhat treacherous middle-ground between other Apple products, as well as other brands' products, as other commenters have mentioned. Too far up or too far down it gets into problematic placement.