IPhone :: Can't Send IMessages To Contacts Containing Both An Email And A Phone Number

iPhone 3GS
model: MC637C
iOS version: 5.1 (9B176)

This issue started with the last iOS update and has affected not only my phone, but my wife's and father in law's as well (we all have the exact same model) When I attempt to send a text message to my wife, my phone suddenly won't send imessages anymore. Only text. I have tried rebooting my phone, and my wife's phone. We have even tried wiping our phones and restoring them from backups. The problem still persists, wether we are at home connected to wifi or out of the house on 3G. The only way I have managed to send my wife an imessage was by creating a new contact with ONLY her e-mail address. That only worked once. since then, its trying to send everything as SMS again.

This is unacceptable as we live in an area with very poor celular coverage and rely heavily on wifi connections, therefore we won't receive an SMS until our phones get access to the celular network. All other apps and phone functions are working correctly across all 3 phones mentioned. On both my phone, and my wife's, I have double checked to ensure that iMessage is still turned on. I suspect that this is a global software issue seeing as it only started once we updated our phones to the latest iOS. My question is this:

Prior to the update, we were all able to send iMessages to eachother, regardless of where we were. The only time we'd have an issue is if someone's phone was turned off or not connected to either the celular 3G network or a wifi with internet access (which is natural).

Info:
iPhone 3GS, iOS 5.1, iMessages being sent as SMS instead