1. Voice commands will work really poorly in crowded places. I'm trying to picture how I'd use voice commands reliably in Denver airport.
2. Any sort of holographic projection thing is going to require something to project on. For privacy reasons you'll often want something you can hold up to your face, and there are many surfaces that would be impolite to use for a holographic keyboard. If you have something you're holding up to your face, now you have to hold the watch steady relative to it... you'd be better off with a detachable LCD screen. At which point you might as well put the phone hardware in the LCD screen instead.
3. Again, ergonomic factors dictate that a watch is not more convenient than a phone for making calls. My watch has one button on the front and four out of the way on the sides. More buttons on the front would make it harder to use (it is typically pressed blind, sometimes while wearing gloves, usually while very tired and out of breath, and for my purposes I need fairly precise timing). A phone needs... a numeric keypad! A device with an effective keypad and be easy to talk into, something good enough that I'd prefer it to my landline, would have to be big. You could have a Bluetooth thing that looks like a phone or a headset or something... but, again, you might as well just make that the phone instead. If you get a call on your watch-phone and don't have a headset with you, what can you do about it? You just get a ring, and maybe you can listen to the message.