This is a code snippet to control UITextView's contentInset.bottom and scrollIndicatorInset.bottom when iPhone's keyboard status is changed to visible or hide.

gistfile1.m

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    NSNotificationCenter *notificationCenter = [NSNotificationCenter defaultCenter];
    [notificationCenter addObserver:self selector:@selector(keyboardWillShow:) name:UIKeyboardWillShowNotification object:nil];
    [notificationCenter addObserver:self  selector:@selector(keyboardWillHide:) name:UIKeyboardWillHideNotification object:nil];
}

- (void)viewDidDisappear:(BOOL)animated
{
    [super viewDidDisappear:animated];
    NSNotificationCenter *notificationCenter = [NSNotificationCenter defaultCenter];
    [notificationCenter removeObserver:self name:UIKeyboardWillShowNotification object:nil];
    [notificationCenter removeObserver:self name:UIKeyboardWillHideNotification object:nil];
}

- (void)keyboardWillShow:(NSNotification *)aNotification
{
    NSDictionary *info = [aNotification userInfo];
    CGSize kbSize = [[info objectForKey:UIKeyboardFrameEndUserInfoKey] CGRectValue].size;
    double duration = [(NSNumber *)[info objectForKey:UIKeyboardAnimationDurationUserInfoKey] doubleValue];
    unsigned int curve = [(NSNumber *)[info objectForKey:UIKeyboardAnimationCurveUserInfoKey] unsignedIntValue];
    
    UIEdgeInsets contentInset = self.textView.contentInset;
    UIEdgeInsets scrollInset = self.textView.scrollIndicatorInsets;
    contentInset.bottom = kbSize.height;
    scrollInset.bottom = kbSize.height;
    
    [UIView animateWithDuration:duration
                          delay:0.0
                        options:curve
                     animations:^{
                         self.textView.contentInset = contentInset;
                         self.textView.scrollIndicatorInsets = scrollInset;
                     }
                     completion:nil];
}

- (void)keyboardWillHide:(NSNotification*)aNotification
{
    NSDictionary *info = [aNotification userInfo];
    double duration = [(NSNumber *)[info objectForKey:UIKeyboardAnimationDurationUserInfoKey] doubleValue];
    unsigned int curve = [(NSNumber *)[info objectForKey:UIKeyboardAnimationCurveUserInfoKey] unsignedIntValue];
    
    UIEdgeInsets contentInset = self.textView.contentInset;
    UIEdgeInsets scrollInset = self.textView.scrollIndicatorInsets;
    contentInset.bottom = 0;
    scrollInset.bottom = 0;
    
    [UIView animateWithDuration:duration
                          delay:0.0
                        options:curve
                     animations:^{
                         self.textView.contentInset = contentInset;
                         self.textView.scrollIndicatorInsets = scrollInset;
                     }
                     completion:nil];
}