The following will wrap long button text, but limit it to two lines.
button.titleLabel.lineBreakMode = UILineBreakModeWordWrap;
button.titleLabel.numberOfLines = 2;
The following will wrap long button text all over your image and outside the bounds of your button. You'll be scratching your head for a while wondering why the numberOfLines property doesn't have any effect.
button.titleLabel.lineBreakMode = UILineBreakModeWordWrap;