Thanks for the replies guys.
All my software is up to date. This never even happened once on my iPhone 3gs and I was using all the same apps as the ones crashing now...
It's just happened with Instagram too..I open it and it immediately turns itself off. :/
When I switched from 3gs to 4...I restored & synced all the apps (only apps, not settings etc) from itunes, could that be the problem?
So it's definitely NOT anything wrong the actual phone, right?