I usually use this method to do pockets inside my bags. It is easy and quick! Prepare lining fabric for your bag. For the 'Blossie Bag' in this tutorial, I cut my lining 9.5" x 21.75". Cut a pocket panel from a contrasting fabric, 8.5" by the width of the lining.
Cut a rectangle of medium-weight fusible pellon, 4" by the width of the lining. Press the pocket panel in half. Place the Pellon on one half of the pocket panel.
Fold the pocket panel over the Pellon & press into place.
Pin the pocket 6.5" from the top of the lining, raw edges towards the top.
Stitch the pocket to the lining using 0.25" seam.
Flip the pocket panel up towards the top of the lining & pin in place.
Topstitch the pocket 0.25" from the bottom.
Stitch the sides of the pocket to the lining, just to keep it in place.
Stitch a series of vertical lines on the pocket panel at desired widths, to fit pens, mobile, iPod etc.
Fit lining to the outer bag & complete as described in the previous tutorial. The inside will look a bit like this:
Hope this makes sense. Again, please email me with any questions.