Getting my new iPad this weekend, I got to try the Cisco (Tandberg) VC Dialer from Sping BV on some of my endpoints. It seems to be working perfectly! It is basically an app that can dial any number from any MXP, C, EX or E series endpoint. You can get it from the AppStore, search for VC Dialer (it is an iPhone app originally). The app is free for a limited number of downloads, after which it will be priced €4.99
You need to be able to reach the endpoints on http (s?), and you need the admin password of the endpoint to be able to control it.
You can only make calls and hang up with the app, it is not a full remote control of the endpoint, but I can still se uses for this.