Just bought a GS last friday and it came with an iphone ram mount on the handlebars, which holds the phone very well. You couldn't put a case on the phone and then fit it as it just wouldn't fit in the holder. My plan is to get a stiff plastic bag of the appropriate size and then just slip it over the top to keep the rain off.
So far I've just had earphones on under the helmet and plugged into the earphone socket of the phone, this allows me to hear the gps prompts from the tomtom software I'm currently running on it. I have an autocom setup I'm in the process of fitting to the bike which will take the output from the phone and feed to the intercom. There's a power socket up on the fairing and I'm planning to just have a short power lead that I'll make up which plugs into the dock connector and have the headphone lead zip tied to the cradle and running to the autocom.
I don't plan to use the phone while I'm riding, as I can't use the touchscreen with gloves on, just the gps function of it. As the phone already had tomtom on it and the bike has the mount, it's just a case of making up a couple of cables and a plastic sleeve and I'm done. Cheapest way to get satnav that I could think of.
J.