Two hot supermodels doing hot Pilates together?! Yes, please!

Hailey Baldwin-Bieber (we can't bring ourselves to use only one last name!) and pal/fellow model Kendall Jenner hit up West Hollywood's favorite hot Pilates studio Saturday -- in fact, it's the same studio Selena Gomez frequents!

The pair both wore sexy Spandex hot pants and sports bras with sweatshirts and Hailey sported her HUGE diamond ring from hubby Justin Bieber.

Kendall made a pit stop after Pilates for some shakes, but sent her bodyguard in to pick them up. Meanwhile Bieber's chillin' in the O.C. at his Laguna Beach Montage residence without Hails. She had to be up in LA for some business, so he stayed behind to continue his regular treatments, though when we saw his yesterday, he didn't look happy at ALL with his wife being away.

Speaking of Justin, we just got in this kinda funny video of our videographer asking Hailey if she "has any cool names for the baby." Ha! Hailey went for some shopping at Fred Segal after his hot Pilates sesh with Kendall. She wore a cute cropped leather biker jacket with a cropped white top (hey, if you're gonna put in the time at the gym, you may as well show off the results!) and jeans. And we LOVE that green G-Wagon, G-Wagon, G-Wagon!