We know what you're thinking; surely the iPhone is far too big for running around with? On its own that's certainly true and any kind of small MP3 player, like an iPod Shuffle or Zen Stone, would definitely be more convenient for general gym duties. Yet, anyone who has an absolute need to take calls while working out may find an iPhone Sports Armband right up their street.
Vitally, it's machine washable - a fairly essential feature for something you'll be sweating all over. It has a suitably strong and flexible Velcro fastened strap that should fit over even the largest bulging bicep, while the screen is protected by splash-proof clear plastic. You can operate the touchscreen through it, too, though it's not as easy as it is on the IceBox Pro. Likewise, you can use the Home button as well, though annoyingly the volume controls aren't accessible.
Strangely, Gear4 has decided to uncover the earpiece and light sensors. We're not sure if this is really necessary given the context. You're not often going to be using the screen while running and if you're going to make and receive calls you'll need a headset, since the microphone and speaker at the bottom are covered.
Despite this, the Sports Armband does its job well enough. A Velcro strap ensures the iPhone won't slip out during use and if you absolutely must use your iPhone at the gym, you will find this very useful indeed.
Though we're not entirely convinced by the iPhone's gym attending credentials, if this is a need for you, Gear4's Sports Armband will do the trick.