https://www.cnet.com/news/iphone-xr-preorders-start/

Thirty minutes after preorders began at the Apple Store online, the only model that wouldn't be delivered on launch day was the 128GB yellow model from T-Mobile. It instead ships in one to two weeks. 

You can preorder the iPhone XR at at: Apple Store | Sprint | Best Buy | Walmart | Verizon | AT&T | T-Mobile.