Fring will work with the rear-facing camera on other Android models, can't imagine them dropping that for the X. Realistically, video calling is a big negative in my phone assessment but if it's very important to you I'd probably either look at an Evo or hold out a bit. My guess is that most upcoming superphones will end up getting another camera squeezed into the face.
Of course if you want video calling from a stationary location (like at your desk) instead of trying to give the people at the other end motion sickness by holding the phone perhaps the mirror trick would be good for you.