You no longer need to carry a Pixel phone to have Google's Duplex book reservations on your behalf. Google has quietly expanded support for Duplex to other Android devices (5.0 Lollipop and newer) and iPhones using Assistant. While it's not certain just which hardware will work at this stage, there are reports at XDA and 9to5Google that Duplex is working on the Galaxy S10 and iPhone.
Duplex still appears to be limited to the US, so you can't expect to book a restaurant table or haircut elsewhere in the world. Even so, it's a big step forward. It's been nearly a year since Google unveiled Duplex at I/O, and it has remained a largely niche feature since it rolled out in November. Although you still couldn't call it ubiquitous at this stage, it's about to become considerably more commonplace.