iPhone & Exchange 2013: need thoughts on managing a corp contact list with iPhone users

Here's the environment: Exchange 2013 back-end (DAG in two different sites), desktop clients using Outlook 2010, and iPhone users with access to a special account containing all Corporate contacts.

Here's the question: we're looking for a SECURE way to be able to share our corporate contacts out to all iPhone/Android users where they can read/view any of those contacts, but *not* add/edit/delete any said contacts.  Currently we've set up a specific Exchange account called "iPhone contacts" and have added that contact list to everyone's iPhones.  The problem is that people can edit, add, & delete said contacts at will.   We need to be able to share or otherwise provide access to an Exchange contact list to all iPhone users WITHOUT them being able to perform any changes whatsoever.  The problem we're seeing is that, because of the way iPhone handles these contacts, any way we try (latest incarnation is the iPhone account) the iPhone user can still add/edit the corporate list.  From Outlook we can restrict access, but the iPhone is the issue.

Suggestions?  Is this something that just isn't possible given our iPhone usage, or is there a third-party app or add-on that we need to purchase to all this?  Gmail/Hotmail/Yahoo lash-ups are *not* an option, and individually managing each and every device is not an option any more (we've been doing this for years because of the iPhones and we're not going to keep doing it moving forward).

Suggestions, thoughts, etc welcome.  We're not going to adopt any mickey-mouse or hacked approaches.  Thanks!
SteveInNV