Hi Pablo!
The initial plan was to include this in the openHAB phone apps but I have zero experience with app design, in either Android or iOS. I started having a play around with HABDroid but got very lost very quick!
Then I came across Mqttitude which did everything we needed.
If you want to build this functionality into the iOS app it would be great - hopefully Victor can find time to do the same with HABDroid, and Till with HABSweetie. I believe presence detection is a very useful/important part of home automation and to have it 'built-in' to openHAB would only make this product more appealing.
The tricky bit is making configuration and setup as simple and painless as possible. Ideally there would be a map where you can drop a pin, specify a radius, a name, and an openHAB item it should be bound to. Then anytime the phone enters or leaves that geofence the specified openHAB item is switched on/off. We should probably allow multiple geofences to be defined, so you might have one for home and one for work for example.
I believe the geofence logic is baked into both iOS and Android, but you will no doubt know more about that.
I would be more than happy to help you with the design and testing of this if you need a hand.
Cheers,
Ben