Sure, the transparent email and the yet-another-dialer brigade are all well and good, but there are a few things the iPhone doesn't do that I really wish it would. Here's a pair of app suggestions that are probably outside the bounds of the SDK and prime fodder for jailbreak developers, but if someone came up with a way to do them that would make it onto the App Store, I can guarantee you at least one customer.
WiFi Master: If you use your iPhone in a major metropolitan area, you've probably encountered the problem I have in New York City -- scores of access points named 'linksys,' 'netgear' or 'default' or a Starbucks broadcasting AT&T's WiFi network on every corner. Join one, just once, and your iPhone insists on hopping aboard whenever it's in range, whether or not the named network is the one you meant to use or whether you've signed into the web portal for the WLAN (leaving you starved for connectivity, as the 3G connection is superceded by the WiFi link).
Tweaking the network settings is generally a no-no for non-Apple apps, but we need help. Give me a quick way to turn WiFi on and off from the home screen, a way to exclude or include access points by MAC address instead of just by SSID (locking out the rogue 'linksys' networks), and instant display of my assigned DHCP address without diving four screens down into the Settings app. Granted, the Devicescape sign-on automation apps are a good start towards this goal (the Easy WiFi for AT&T iPhones app is worth the $0.99 in aggravation reduction) but I need more active WiFi control in this network-dense environment.
As noted in the comments, the jailbreak app SBSettings covers a lot of these use cases; if you're in a WiFi hot zone and you can't take any more, it might be the tool that pushes you to jailbreak your phone.
GotThis?: One of the favored activities of appoholics, when meeting in their secret underground lairs, is comparing screenfuls of cool iPhone apps to see what they might want to download next. It would be easier if these phone-waving sessions could be automated with -- of course -- an app that would compare your installed suite with that of your neighbor's, point out what he's got that you don't and vice versa, show you most-run statistics and then perhaps link you to the App Store if you've gotta have one of those apps right away.
The problem is that the roster of installed apps is not accessible to a sandboxed app running on the phone, at least not under SDK rules; one way to do this would be to scrape the installed app profile from iTunes and then store it, with the user's permission, on an external website (leveraging the existing iUseThis for iPhone, perhaps). Give this app the interface and location awareness of contact sharer & billionth-app Bump, let users tap iPhones to compare installation profiles, and you'd have a fun social networking tool plus an appoholic enabler of devastating proportions.
What's on your app wishlist? Have you seen apps like these, either in the App Store or in the Cydia Store? Let us know below.