I've read elsewhere that iOS 4.3.0 and above will not be able to be jailbroken, is that correct?
If I jailbreak my iPhones now and install and become dependent upon MyWi for my iPad and MacBook Pro while away from home, I want to make sure I am not stuck with what will soon become an outdated OS.
I had to look at the date of your post to make sure it was really now. The iOS is now up to 4.2 and they are all Jailbreakable. In the three years that the iPhone has been around there has always been a JB available for the firmware so I don't see that changing anytime soon. If you JB you will not be stuck just don't update until a JB is available, and the worst case scenario is that you restore your device and use the Apple firmware.