The problem with ALL of these "all things to all men (and women) devices is that you're really in the proverbial if the device:
1. fails to work
2. gets lost
3. gets stolen
The first of these is very likely as the more complicated a device is, the more likely it is to go wrong. The chance of failure rises in geometric proportion with the rise in complexity.
The second of these becomes increasingly possible with the obsession with miniaturisation so that before long (and the miniaturisation rate proceed at the same rate it has been doing) your mobile phone will be so small it will be able to slip through the stitching on your trousers pocket.
The third prospect gets more likely with every development in a mobile phone. If the device contains money (if only in a theoretical sense) again, the chance of theft rises in a more than linear proportion.
My mobile phone is like pj123's. It functions as a phone - nothing else. I want it to remain that way.
What's your objection to using a mobile to pay at the supermarket? It's exactly the same as using any other means of payment. It also cuts down on the stuff you carry around if you can use one device for several different functions.
If it catches-on I don't suppose it will take the criminal fraternity long to find ways of exploiting this. Also there is no such thing as a mobile network that works everywhere. A mobile is useless without a signal as we all know.