Some people take the promise of the iPhone’s multi-function nature seriously; all they have is an iPhone and they use it for everything they used their iPod for—even going so far as to take it out for a jog. But let’s be honest: if you want to take your iPhone running, you’re going to need a special case, like Belkin’s $30 Sport Armband for iPhone.
A black armband made from neoprene with a velcro fastener, the Sport Armband features a large pouch for the iPhone; a clear, flexible-plastic window the length and width of the iPhone’s display lets you use the multi-touch interface while the phone is in the case. The top of the pouch features a slit through which you insert the iPhone and leaves the headphone jack and Sleep/Wake button accessible. On the other hand, you don’t have access to your iPhone’s dock-connector port or Ring/Silent switch. The volume controls are similarly covered, but subtle + and - signs on the side of the case overlay the button locations, letting you press them through the case material. There’s also a small, handy pocket in the armband for storing a key.
While the Sport Armband’s construction is pretty good, during my testing I took issue with some of Belkin’s design choices. For example, the iPhone’s volume buttons are difficult to find and operate through the case when you aren’t moving, and even more so while running. One could argue that this is at least partly a failing of the iPhone’s design, but the Sport Armband certainly does nothing to overcome the problem—and, in fact, complicates it by giving only the barest of indications of the buttons’ location. I also had some trouble adjusting the armband, as the velcro on the strap would get caught in the metal buckle.
From a protective standpoint, the Sport Armband will likely get the job done. The plastic window should keep your iPhone’s screen scratch-free and, hopefully, having your iPhone attached to your arm will obviate the need for heavy-duty shock protection.
The truth is that the iPhone isn’t ideal for exercise use thanks to its size and interface. Belkin’s Sport Armband doesn’t magically change this, instead providing a functional case for those determined to go jogging with their iPhones.
I have one of these and do take it jogging frequently in the Berkeley Hills. My biggest issue is that it's hard to see the screen when it's strapped to your arm -- if I want to change tracks or answer a call while running (yet to actually happen) I can't quite make out the icons at a vertical orientation. But like you said, it does the job.