Just a fun & serious question - which of your day-to-day problem would you like to get solved by mobile? It may not be something very big or critical - but any small stuff you'd like to get done with your mobile to give you great convenience! Any wish list?
I would love to find a mobile phone that lets me contact others and communicate with them by speaking into it, and have them be able to speak back to me. To date, I have not found a mobile that does this well.
There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors