For most users the EZ-Key or the Simple Feather versions of this project would give you excellent access to your iOS device. Also note that such access can be obtained by using commercially made BLE devices and AT switches. However as a maker and hobbyist we can go above and beyond those simple ideas to create really powerful and effective devices using the higher concepts such as a multimode application possibly with chorded functionality.
Use your imagination and creativity to come up with the ultimate device which will give the maximum benefit to a disabled user.
Such a device has allowed me to go beyond simple things like posting on Facebook or playing iPhone games. Recently I was hospitalized and on a ventilator where I could not talk. I was able to type messages into the "Notes" application on my iPhone to talk to the doctors and nurses who were caring for me. I would've been lost without this device.
Naturally this is a simple solution that could have unknown bugs. On occasion my iPhone has spontaneously disconnected from the BLE device or accidentally turned off of switch control so you should be careful not to rely on such devices under "life critical" circumstances. But for everyday use, and when needing to communicate under difficult circumstances like I encountered, this is an excellent solution.
We recently come across an excellent iBook by iOS switch control user Christopher Hills. This is a free download on iTunes. Unfortunately like all iBooks it can only be read on a iOS device such as iPhone, iPad, or iPod touch but if you didn't have one of those you would not need his book anyway. This is a very detailed guide on how to use iOS switch control and is a must read for anyone who's using this feature. https://itunes.apple.com/us/book/handsfree/id1040716154
Addendum: Here are some additional YouTube videos I created related to iOS switch control.