It's a tricky thing.. on one side, you could argue that phone numbers are just as open to being found in a pocket planner as a smart phone, and that was the justification that was used in this case. It's been pretty much common practice. That has been going on for a long time.
Problem is, you are slipping that 'open book' rule onto a device that literally is a computer. And I know a LOT of people who use their smartphones for a lot, tracking purchases, using things like Foursquare to put their locations on spot (I've abused the 'coupon' options a few times to get cheaper copying, and other things with a few well planned 'check ins' a few days/weeks ahead of when I needed them). Would you allow the cops access to your checking account, bills, emails, photo collections, and anything else you have on it without permisison?
I can see both sides of the case and I'm a bit split on it myself.