I have that same phone. Never used anything from PLX devices but have seen other people working on apps that do the same thing. What do you get for $105? I have seen obd2 bluetooth adapters for $50 that work. Don't now about the ones on ebay for less then $30.
I considered what ZOMGVTEK said but I never leave home with out my phone so having it to use in the car is not a problem. The last time I left home without my cell my car broke down.
There are some nice features you get with android phones you don't get with the ScanGauge II, or UltraGauge such as GPS and easy updating of software right on the phone. The phone tells you when ever there is an update for any app installed. Can the ScanGauge II, or UltraGauge log all data recorded and transfer it to a computer or directly to the internet? Not that its needed but the Samsung Galaxy S can display 16 million colors and has enough memory and processing power to make it look like a super computer compared to the ScanGauge II, or UltraGauge. The large screen size is also a plus and the Samsung Galaxy S is not the biggest screen size for an android phone.
Do you loose all data from the ScanGauge II, or UltraGauge if your battery dies? Had a problems recently do to a weak battery, trip odometer kept resetting itself very annoying.
The only real limitation of android is the programs written for it.