My cellphone works while the power is out too.
Sure, as long as the batteries last and you have useful reception in your current location (and the base station isn't affected by the outage). These are relevant concerns with a cell phone, while they matter little with a traditional land line.
You act as if smartphones somehow don't do their jobs, or that they're all massively unstable which is total bullshit.
That's a matter of opinion. Do they crash every five minutes? Of course not. Do they crash often enough to be annoying and potentially dangerous? Yes, every major mobile OS platform has had this problem at various points in recent years. Given this is a device you might need to call an ambulance one day, none of the major platforms has a great record on stability.
As for doing their jobs, there have been a few antennagate-style stories over the years, where some fundamental design flaw has undermined the basic functionality of the device as a phone. It seems popular to make thinner smartphones with larger screens that then bend or break in your pocket lately.
Modern smartphones seem to be about on par with PVRs and so-called Smart TVs. They do their job up to a point, and they do offer some advantages over the devices we used before. On the other hand, they are also trying to do too many different things to do any of them really well, they often try to be a bit too clever about how they do them too, and at some point these things affect the reliability of the system and/or raise security and privacy concerns.
I often have a feature phone in my pocket and a tablet in my case/bag, and I have yet to find anything I want to do while I'm out and about where a typical modern smartphone would be better at it than one or other of the devices I actually use. YMMV, but I'd be genuinely interested to hear of any common tasks that a modern smartphone really is better at than other widely used but more specialised devices, because I can't think of any myself.