Other skills or software or services you will need
As well as iPhone app development software, you will need an Apple developer account to be able to publish a game for iOS. This costs $99/year and gives you access to the SDK, developer documentation (including guidelines), developer forums, iTunes connect (for submitting and monitoring your app) and areas for filling in and maintaining agreements for publishing, tax etc. with Apple.
Depending on your title you will need at least 2D image editing/creation tools such as Photoshop, The Gimp, Pixelmator, Illustrator and maybe 3D apps like Maya, or Blender 3D.
Even if you are not the artist(s) you may well need these tools to check art you get from team mates or contractors you use to generate your art.
Audio is an often under rated or forgotten part of game development. Whilst you can source plenty of high quality royalty free audio on the net, you will probably still need to be able to level, edit and convert the audio for your tool of choice, again the options are many from free to paid, look for tools such as Audacity (free), Sound Forge etc.