Apple iPhone/iPhone 3G (User manual) - Manual (Page 117)

Chapter 8 Settings 117
Photos
Use Photos settings to specify how slideshows display your photos.
Set the length of time each slide is shown: Choose Photos > Play Each Slide For and
select the length of time.
Set a transition effect: Choose Photos > Transition and select a transition effect.
Set whether to repeat slideshows: Choose Photos and turn Repeat on or off.
Set photos to appear randomly or in order: Choose Photos and turn Shuffle on or off.