Windows Phone 7 has various pre defined hubs available on the home screen (start  menu) including calls, messages, pictures etc. You can easily rearrange these items in the start menu based on your preferences. For example, if you use the picture hub more frequently you can bring it above the calendar and so on. Rearranging hubs on the start menu is pretty easy task.

To rearrange items, click and hold the item you want to move and you can see the item highlighted with a pin. You can drag the item to desired location and then pin it back.

Related: How to Change the Theme and Background Color in Windows Phone 7

Here is a short video of rearranging items in start menu in Windows Phone 7.