iMessage Issue with One Contact? (iPhone 5 iOS 6)

Hey Everyone,

There is one contact in which my iMessage will sporadically "die" and will fail to send as an iMessage. Whether I'm on WiFi, LTE or 3G (even with 3+ bars of WiFi), the message bar at the top after I click send will zoom past and then the message will stay blue for about 5 minutes, after which I check back and it ended up going through as an SMS.

I have tried resetting all network settings, resetting all settings, and even restoring my iPhone as a new iPhone. None of these worked.

I have also turned On/Off iMessage, WiFi, and Airplane mode. These are all temporary solutions. I made sure that in my iMessage settings only my number is selected as a send/receive option, and completely turned off iMessage on my computer (Mac OS X Lion).

I did not have these issues running iOS 6 (betas) on my iPhone 4S.

Have you guys faced any similar problems? Come up with any solutions?

I thought that may be the case, but I've had her (my girlfriend) perform all the same "fixes." On her end, the issue only occurs when texting me as well.

Anyone have any idea? We have both swapped out and got new iPhone 5's from Apple now.