What if you get a call?
What if you get a text?
I just think that because multitasking isn't fully utilized on the iphone. Will "quiting" your tomtom to go answer a phone call or text ruin your tom tom and you have re-input the data?
a) iPhone OS 3.0 allows apps to run in the background so no it won't cancel your route
b) not sure what the law is where you are but here it's illegal to use a mobile phone whilst driving, unless you are using a Bluetooth headset for calls or a fitted in car system. Pretty sure it's the same across the EU.
c) you should not be reading texts whilst driving at all.