It is possible but will raise a warning when the ticket is scanned. (Yes I tried ...)
There's a trick that allows you to cheat the system and not pay for the ticket unless it is scanned but I find it rather dishonest so won't give it ;-)
Layar : Funky augmented reality app, taps into various resources to show you places of interest around you with little dots on your camera screen. 3GS
Cyclopedia : Same as above really, but only uses wikipedia as a source, so not quite as good. 3GS
Mobility Finder : Find your nearest mobility car, bit basic at the moment, it only finds the nearest cars and then has a button to phone mobility themselves, but if they keep developing it to make it something like the SBB app, it would be fantastic.
Amazon (UK) have just released their app for the iphone. You can search their extensive online store (+ third party sellers), add items to your wish list, buy and most importantly read other customer reviews. I can see this being very useful the next time I'm in Saturn, Interdiscount etc..
When you exit fring without chosing the option to "Go Offline" you still get messages via push notification even when fring is not running....to reply you can launch fring and exit again.
You dont have to keep the applicaiton running in order to be connected
1). Oxford Translator German Travel Pro (5.50 Fr.) - for phrases, grammatically numbered (i.e. 1, 2, 3, etc.) with correct pronunciations; and
2). German-English Translation Dictionary by Ultralingua (22.00Fr.) - it's gone up since I've purchased it, however it's worth having even at this price.
These apps don't replace actually German courses, but they have proved to be very helpful to me.