No suggestions for iPhone, but for Android I use the following:
DOF Calculator https://market.android.com/details?id=com.aimenrg.dof
A nice clean depth of field calculator, written by a CR forum member.
Photo Tools https://market.android.com/details?id=be.hcpl.android.phototools
A bunch of handy little tools all in one app. DOF & Hyperfocal Distance, Field Of View Calculator, Exposure Reciprocation, Flash Exposure Calculator, Multiple Exposure Compensation, Sunny 16, Sunrise/sunset, Graycard, Color wheel & temp chart, Moon Phase, Sharpening & Enlargement, Photo Guide, Gallery For Inspiration, and several more.