We've gotten questions from readers asking if iOS 4.3 will be compatible with all iDevices. Sadly, the answer is no. The public release of iOS 4.3 that Apple announced at their iPad 2 event will only work on certain iDevice generations.
Most notably, 4.3 will not be installable on the Verizon iPhone. Because the Verizon iPhone runs on a different baseband and has different bugs to fix, Apple has to release a separate 4.3 build for that device. (Which they haven't announced yet.)
Hopefully your iDevice isn't on the 4.3 incompatibility list...