I ordered one of these for my son's xt250, but once I saw it, I ordered another for me to use on the S10 as a tank protector and to carry incidentals. It has strong magnets and had a nice pouch for the cell phone right where you can see it for incoming calls.
http://www.motorcycle-superstore.com/1/4/71/1938/ITEM/Joe-Rocket-Manta-Magnetic-Tank-Bag.aspx
http://www.motorcycle-superstore.com/1/4/71/1938/ITEM/Joe-Rocket-Manta-Magnetic-Tank-Bag.aspx