The year is 2007 and your friend pulls a shiny new iPhone out of his pocket. It's the first one you've ever seen, and you stare agape as he lovingly taps the screen. A feeling starts to bubble up inside—contempt?
Mobile forms tend to have significantly more constraints than their desktop cousins: screens are smaller; connections are slower; text entry is trickier; the list goes on. So, limiting the number of forms in your mobile applications and websites is generally a good idea. When you do want input from users on mobile devices, radio buttons, checkboxes, select menus and lists tend to work much better than open text fields.