Programmatically change UITextField Keyboard type

There is a keyboardType property for a UITextField:

typedef enum {
    UIKeyboardTypeDefault,                // Default type for the current input method.
    UIKeyboardTypeASCIICapable,           // Displays a keyboard which can enter ASCII characters, non-ASCII keyboards remain active
    UIKeyboardTypeNumbersAndPunctuation,  // Numbers and assorted punctuation.
    UIKeyboardTypeURL,                    // A type optimized for URL entry (shows . / .com prominently).
    UIKeyboardTypeNumberPad,              // A number pad (0-9). Suitable for PIN entry.
    UIKeyboardTypePhonePad,               // A phone pad (1-9, *, 0, #, with letters under the numbers).
    UIKeyboardTypeNamePhonePad,           // A type optimized for entering a person's name or phone number.
    UIKeyboardTypeEmailAddress,           // A type optimized for multiple email address entry (shows space @ . prominently).
    UIKeyboardTypeDecimalPad,             // A number pad including a decimal point
    UIKeyboardTypeTwitter,                // Optimized for entering Twitter messages (shows # and @)
    UIKeyboardTypeWebSearch,              // Optimized for URL and search term entry (shows space and .)

    UIKeyboardTypeAlphabet = UIKeyboardTypeASCIICapable, // Deprecated

} UIKeyboardType;

Your code should read

if(user is prompted for numeric input only)
    [textField setKeyboardType:UIKeyboardTypeNumberPad];

if(user is prompted for alphanumeric input)
    [textField setKeyboardType:UIKeyboardTypeDefault];