NQ Vault is a popular “encryption” program for Android and iPhone. It is listed as a “free download” but that is really only a trial version. To keep using NQ Vault, the user must pay to keep using it. Details may be found at http://www.nq.com/vault.
One problem: at least the Android version doesn’t encrypt anything. An article at https://ninjadoge24.github.io/#002-how-i-cracked-nq-vaults-encryption shows how to easy reveal anything that was supposedly encrypted with NQ Vault.
The iPhone version apparently hasn’t been tested yet.