i use the topeak ridecase for my iPhone.but instead of lockign the mount to the headtube, i got the accessory handlebar mount and nount it on my toptube... it looks ugly, but gets good gps signal plus i can see the screen without taking my hands off the handlebars...

i carry a phone with me on rides so that my riding buddies can call me and tell me to speed up else they will drop me...