EDIT: So, by now (2016) I've made one for Android myself with a friend. See DSO Planner - the best handheld digital star chart ever built!
HTC HD2. When in the field, I'm always carrying it enclosed in the OtterBox defender case which have a plethora of useful properties:
- It provides the best protection for the phone from elements. Including moisture, dust, and falling.
- It takes just 15 seconds to open it and insert a piece (or two) of a red film behind the screen protector of the case over the smart phone screen and make the device completely dark-adaptation friendly.
- The belt clip construction of this case is also an amazing piece of precise engineering. You can securely mount the phone in its solid wrap-around type cradle instantly, face up for work, or down - for total protection of the screen.
- The clip has ratcheted pivot point helping to orient the phone on the belt.
- The belt clip mechanism can also be switched to a TV stand mode.
- It's not covering any ports, so you can charge the phone while it's on the belt clip (or if used as car dash cradle).
- There are 3 mounting screw holes on the side of the cradle, suitable for a really tough mount designs (I'm not using them with this one, though).
I had it securely attached to the OTA with a couple of 1/8" bolts, in the thoroughly measured sweet spot between the focuser and the finder scope eyepiece. The location provides some freedom for rotation of the phone in the cradle and for shifting it up and down a little along the "belt" (for comfort at the either eyepiece). The belt clip of the cradle fits under the belt very snugly, thus it's not only very reliable but also allows to use the TV stand mode when necessary to add a rolling direction of freedom (good to work at the finder's EP).
GSSP star party (black LPZ) revealed the amazing efficiency of such a setup. In tough situations (when working with the newly installed Telrad) I could just take the phone out from the cradle and use it in the hand. It was very convenient to power the phone right in the cradle from the external car battery sitting at the base. Also the phone was working well as a dim red flashlight.
NOTE: The orange tape on top of the phone is a piece of orange duct tape dimming the charging LED of the phone, a must for the dark adaptation protection.
Since then I have switched to Android and developed one of the best astronomy sky chart apps ever for it the DSO Planner. The new app, new larger smartphone, the belt mount works with them without any modifications, it's just the same belt any belt clip is designed for. Thank you OtterBox!
I can see the chart with one eye and the EP FOV with another simultaneously, from the distance, or take it to the Telrad for side by side matching of the view for precise zero magnification pointing to invisible to the naked eye objects. The ultimate solution!