The question is simple: what old phone are you ditching to get a new iPhone 5? Is it a previous generation iPhone like last year's iPhone 4S, or an even older iPhone like iPhone 4, iPhone 3GS, or iPhone 3G?
Or is it an Android phone, like the Samsung Galaxy S3 or S2, or Galaxy Nexus or Nexus S? Or an HTC One X or Nexus One? Something from Motorola like the RAZR? Another Android phone entirely?
Maybe a Windows Phone like the Nokia Lumia 900 or Lumia 800? Or a different kind of Windows Phone? Something by BlackBerry perhaps, like Bold or Torch or Curve? A webOS device like the Pre?
Or could the iPhone 5 be your very first smartphone? Vote up top and give me the details on what you're switching from and why in the comments!