Chipper Whether or not it's "right", it happens, and often there is no alternative. I'm not looking to get into a debate, only to know if such a feature has been implemented, or if not, information on how to ask that it be implemented.
Crossing back into the US? There's a chance that your phone will be searched, and if you refuse, you can be denied entry, even if you're a US citizen. Also, remember that border patrol has authority up to 100 miles from the border.
I've seen it happen at a job, where a fellow employee was made to unlock her phone for her boss on the threat of being fired, and in the US, this is totally cool and legal.