iPhone 4s auto-lock greater than 5 minutes

[Fletchi18]

We are using iPhones here connecting to our Exchange 2010 environment and users are asking if the auto-lock function can be increased past the 5 minutes that the phone offers. Our policy is set to 30 minutes, so it doesn't seem like it's being restricted by that.

Is there a way to set the auto-lock to 10 minutes? Or 15 minutes?

Any help with this is greatly appreciated.

Thanks!