Something that would be nice, would be really nice from a mobile phone - just a simple device that you can make calls on, use a hands-free set and, hopefully, listen to MP3s - is a standard headset socket.
I'm serious. Getting away from Bond-esque dreams of combining GPS, broadband speeds, a web browser that can do full flash and AJAX and everything else, a high-speed text input system (however you want to do it) and, well, let's say a 5MP camera with an optical zoom (why aim low?), let's get back to basics.
I would like to be able to buy a good set of earbuds to replace whatever came with the phone, maybe a wired handsfree to save on batteries or something, and be able to plug them in.
At the moment, my Samsung uses a different socket to my girlfriend's Samsung, and I can't use the earpiece at the same time as the USB cable or the charger. Neither of them share a socket with any Sony-Ericsson, Motorola, old Siemens, BenQ, HTC, O2... So you're stuck with whatever you get given, which is frequently pathetic and, if you should lose it or not get given one to begin with, expensive.
I would like (although I don't hold out much hope) for my next mobile to use the same headset socket now used by radios, mp3 players, and computer speakers.
We can all dream.