If you're planning to get the new iPhone 5, you'll likely want to order it tomorrow to get it as soon as possible. There have been rumors that supplies may be constrained initially because of the new in-cell screen technology. According to news reports, preordering will start tomorrow morning at 12:01 a.m. on Apple's website, as well as the websites of the three carriers: Verizon, AT&T, and Sprint.
If you're trying to decide which carrier to go with, be sure to check whether they have 4G LTE in your area. Also, FaceTime is now possible over 3G and 4G networks with the arrival of the iPhone 5 and iOS 6. BUT ... the carriers may not allow it.
According to GottaBeMobile, Verizon and Sprint have confirmed that you'll be able to do FaceTime over their network regardless of your data plan. AT&T, however, is limiting FaceTime to those customers on its Mobile Share plan. Another consideration is that Sprint is the only carrier offering unlimited data for the iPhone 5. But they also have the smallest 4G network, so be sure to check whether they offer it in your city.