The planned ship dates for all of these devices was October 23, but some are already backed up into November. In some cases, it depends on the configuration that you choose. At the time of this writing, some iPhone 12 and iPad Air configurations are shipping later, but others are still listing October 23 as the ship date. On the other hand, every iPhone 12 Pro configuration we looked at promises to ship either later in October or sometime in November.
Additionally, Apple seems to have normalized the cost of the iPhone across all carriers after an initial uproar about the phone being announced at a slightly cheaper price point on AT&T and Verizon.