I've got one of these, I think they're meant for pushbikes, but its secure enough and I had the same one for my iPhone before, no problems with it's security I used it all the time and on pretty long trips.
Only problem is mounting it on, I've mounted mine on the H-frame, using some rubber and duct tape to give the H-frame width to clamp the bracket on, I'll get some photos for you later.

 

check out www.ram-mount.com they make some pretty decent gear for mounting things from phones, to gps', to cameras.

 

sweet pics would be great, i was thinking of on like that but was sure how the bar thickness side of it was going to work, and a little paranoid that the phone may jump out of the clamp... but i guess that may be just me, if it aint bolted down it aint secure

 

RAM MOUNTS!!! they even made a cupholder mount for your iPad... those dudes have everything.

 

Here's some photos of how I've got mine setup, it could be neater, but the rest of my bike is a mess at the moment so I'm not too concerned

 

no cbr250 listing from ram mounts...
Thanks for the pic's, rubber hose should work id think to get a straight edge on the clamp.

 

I was going to get a bar that runs between the h frame and would let you then put on one of the mounts above with the top of the phone just under the screen.
You would be able to see it easily as opposed to looking down at the tank and it will be safe (enough) tucked out of the wind etc

 

have a ram mount ball bolted to the steering stem nut works great for sat nav

 

cable ties!