I use a Garmin eTrex Vista with City Navigator. Waterproof, drop proof. Easy route downloads from ridewithgps.com. A bicycle mount is available. If buying new, I'd look closely at the touch screen models.

That being said, I usually turn it on for just a few minutes to point the way, longer of course for the rare time I am navigating through a town large enough to need some turn-by-turn. The Vista elevation feature is nice when in mountains.

This article may be helpful.

My cell phone is an inexpensive flip phone.