Since I now have wireless internet access on a truly mobile device (new Blackberry), I took a quick look to see if there are any astronomy applications for it, and I found MicroSky (v3). It's pretty cool, and it's free. Essentially it's a small Java application which can run on many mobile devices, as long as they can access the internet to get the sky data from SkyServer. SkyServer is a free astronomical database service that you can also use on a regular web connection. MicroSky is tailored to the small displays and limited computing and control capabilities of mobile devices. You need to set up a free account on SkyServer to use MicroSky. You log into it on your mobile device to get the pictures you want sent to your screen.
So how is it? Well, compared to Stellarium, it's more of a star chart than a planetarium, but it's a dynamic little star chart you can hold in one hand anywhere you have a cell phone signal (like the middle of some big, dark field). It's got features for defining where you are and what you want to see. It even has orientation aids on the screen - point your phone south and two circular "altitude/azimuth" icons help you to line up your display with the part of the sky it is displaying. Simple and clever, and explained with pictures in the small manual (the screen shot above doesn't include these, but see below). It has GPS and BlueTooth support too, but I haven't gotten that far with the Blackberry yet!
If you would like to see how this works before downloading and installing the (tiny) files, there is a working demo of MicroSky v2 here. You click the buttons of the on-screen phone as if you were pressing them on a real device (except you get to use your keyboard to type the login info). You can use the demo account, but it's better to create a free account so you can set your own location. This will also show you the altitude/azimuth icons.