Sew a casing on side of bag & pull the strap through, the tie in knot! == Ribbon and Faux Suede Soft-Touch Shoulder Bag with Renaissance Ribbons
Ribbon Fold-over Wallet with Renaissance Ribbons - might adapt to hold cell phone as well.
Ribbon Flap Shoulder Bag with Renaissance Ribbons
Mesh Zippered Sport Pouches with Elastic Trim
Fold-Over Zipper Top Purse tutorial -
Cool approach to an adjustable strap (Ribbon Flap Shoulder Bag - free pattern found on
Re-imagine & Renovate: Renaissance Ribbons' Metro Bag (and Giveaway)
All wrapped up: Patchwork-y Bi-fold Wallet Tutorial-original instructions.
Quick DIY Gifts You Can Sew - Mini Messenger Bag - Best Sewing Projects for Gift Giving and Simple Handmade Presents - Free Patterns and Easy Step by Step Tutorials for Home Decor, Baby, Women, Kids, Men, Girls http://diyjoy.com/quick-diy-gifts-sew