I picked up an "Arkon Bicycle Mount for iPhone" from Amazon several months ago, and it's worked out OK for me thus far. I just checked, and it looks like they've dropped the price considerably since my purchase; It's less than $8 atm. To my mind, it doesn't hold the phone quite as securely as I'd wish, so I always add a little insurance with an extra added rubber band in place. Seems to work, as about three weeks ago I got broadsided by a car running a stop sign. Knocked me complely off the bike, cracked a chainstay, but the mount stayed on the bike, and the iPhone stayed on the mount, and was totally untouched.