Creating a Mask in Photoshop - filling a font with image

1: Copy an image to the clipboard and create a new document with transparent background contents - File | New .
2: Click Create New Layer on the Layers palette. Insert image from the clipboard - Ctrl+V.
3: Switch to the bottom transparent layer, select the Text tool, and enter the desired text.
4: Alt-click over the line separating layers on the Layers palette.

Watch the effect. - Like, below