As the owner of a first-gen iPhone, I'd say the feature it's most calling out for is GPS. If I was forced to choose between 3G data speeds and GPS tracking, I'd opt for GPS and tolerate EDGE data speeds. Maps on the iPhone is awesome - although admittedly slow over EDGE so, yes, I'd really like GPS *and* 3G. I love the way Maps integrates Google Maps with my address book and then lets me generate turn-by-turn directions, but GPS for proper satellite navigation is the missing piece in the puzzle. Hopefully first-gen iPhones upgraded to 2.0 firmware will be able to access an external GPS adaptor for in-car navigation, perhaps via Bluetooth.
3G is kind of a given in the new iPhone, but why can't I use my first-gen iPhone as a broadband modem for my notebook? The practice is known as tethering and practically every other high-end phone on the market supports this feature. Some say the lack of tethering is so AT&T users in the US don't take advantage of the unlimited data plans, but how about thinking about the rest of the world for a change? If this is the reason behind disabling tethering, the move to 3G isn't likely to encourage Apple to change its mind. While they might be generous with mobile bandwidth in the US, telcos in most other countries (like Australia) are highly unlikely to offer unlimited data plans with the iPhone, so they'd probably see tethering as a great way to sting users for excess data charges.
3. Option to disable data connectivity
One of the biggest risks for iPhone users is data bill shock - not only because the iPhone makes mobile data services more tempting to use, but because the iPhone starts chewing through mobile bandwidth as soon as you take it out of the box. When the phone goes to sleep it shuts down wifi to save power and uses the mobile phone network to monitor your email and run other background processes - racking up your data bill. On an unhacked first-gen iPhone there is no way to disable this (short of changing the APN), which is a huge problem if you're not on an unlimited data plan. On a hacked iPhone, an app like Boss Prefs lets you disable data access yet still make calls and send SMS.
4. Wireless syncing
I shouldn't need to physically attach the phone to my computer to transfer music and podcasts to the phone. Even the ability to sync with a Google Calendar over the air would be a step in the right direction.
5. Subscribe to podcasts wirelessly
Similar to demand number 4, I want my iPhone to automatically suck down my favourite podcasts and vodcasts from the internet each week so I don't have to sync them from a computer at all. Sure it's easy to connect your phone to your computer, but I want to keep the charge cradle on the kitchen bench, not connected to a desktop computer. Of course I then want an option to tell the iPhone to only suck down podcasts via wifi, so I'm not racking up a mobile data bill. The ideal situation would be for the iPhone to wake up in the middle of the night, check for a wifi network and the automatically pull down my podcasts of choice.
Some might say I'm already asking for too much, but I'd got a few more demands of the crew at Cupertino.