I have been working on this for about 2 days, so i thought i share my learnings with you.

The question is: Is it possible to make the width of a cell in a grouped UITableView smaller?

The answer is: No.

But there are two ways you can get around this problem.

Solution #1: A thinner table It is possible to change the frame of the tableView, so that the table will be smaller. This will result in UITableView rendering the cell inside with the reduced width.

A solution for this can look like this:

-(void)viewWillAppear:(BOOL)animated
{
    CGFloat tableBorderLeft = 20;
    CGFloat tableBorderRight = 20;

    CGRect tableRect = self.view.frame;
    tableRect.origin.x += tableBorderLeft; // make the table begin a few pixels right from its origin
    tableRect.size.width -= tableBorderLeft + tableBorderRight // reduce the width of the table
    tableView.frame = tableRect;
}

Solution #2: Having cells rendered by images

This solution is described here: http://cocoawithlove.com/2009/04/easy-custom-uitableview-drawing.html

I hope this information is helpful to you. It took me about 2 days to try a lot of possibilities. This is what was left.