The switch to the space-efficient Lightning connector poses the biggest loss to iPhone users, but beware of other gotchas.
For example, the iPhone 5's deeper screen (1,136 pixels) is unknown to most apps, so they won't extend to take advantage of it. Instead, you'll see a border where the old screen ended (960 pixels), though the width remains at 640 pixels. Developers can update their apps to sense the device and change the screen geometry accordingly. Apple says it will make that update for its apps by Friday, but that could take weeks or more. In the interim, you'll have an experience gap across your app library. That fractured user experience is very un-Apple.
If you're an international traveler, also be aware that the iPhone 5 uses the new Nano SIM standard, and your existing SIM cards won't work in it. Carriers have yet to produce the new Nano SIMs; until they do, you won't be able to swap SIMs to use the iPhone 5 in other countries.
Finally, there's been a minor firestorm of complaints in social media and the blogosphere noting that the CDMA versions of the iPhone 5 for Verizon and Sprint don't allow simultaneous use of voice and data. That's true, but it's been the case in the two previous CDMA iPhones (the 4 and 4S). At its core is how the carriers deployed CDMA, dedicating the whole LTE channel for either voice or data, not splitting it. That allows for better speeds, but limits flexibility. That's why if you use the Find My Friends feature in iOS to track an iPhone user, he or she disappears from monitoring while talking on the phone.
It's not an Apple design flaw, but it does reflect Apple's choice not to use the workaround employed by many Android devices: They switch to a 3G channel for voice while LTE data is active, in essence using two simultaneous connections. That also means they need two active radios, but Apple has included just one in the iPhone.
It's not a lost feature, but it could be considered a lost opportunity. It's also a problem that Verizon and Sprint created, which they could solve by changing their LTE network setup -- clearly what Apple thinks should happen.
The lost capabilities in the iPhone 5 are all ones that money and/or time will resolve. But if any are critical to you, be sure to time your upgrade with the availability of the solution -- and your ability to pay for it.
One piece of good news: I can attest that Apple's new EarPods earphones are really nice-fitting and sound very good -- and they work with any iPhone, iPad, or iPod you already have!
A side note unrelated to the iPhone 5: Thanks to BizTech Magazine for naming my Mobile Edge blog as one of the 50 must-read IT blogs in 2012.
This article, "What you lose if you switch to the iPhone 5," was originally published at InfoWorld.com. Read more of Galen Gruman's Mobile Edge blog and follow the latest developments in mobile technology at InfoWorld.com. Follow Galen's mobile musings on Twitter at MobileGalen. For the latest business technology news, follow InfoWorld.com on Twitter.