I can confirm this works. Using the earphones and earphone mic, on Ipad2 Facetime to any other device, it works fine. Unplug the earphone and the called party can't hear you. The exact same issue exists, and the exact same remedy works, when calling via Skype. Ipad2 IOS5 calling Iphone4 with IOS 4
I tried to use my earphones with the built-in mic and it worked perfectly. When I unplugged them, it stopped working. For those of you waiting for a software fix, you can try the earphones trick and at least get it to work. Good luck.