Haley James Scott (Lenz) and Brooke Davis (Bush) were the first to join the call, and the pair passed the time discussing the former's music career before her kids, Jamie and Lydia, distracted her.
"Do not draw on the walls! Jamie! Go play with your sister! I'm serious!" Haley yelled at her off-camera kids.
Once Peyton Sawyer (Burton) signed on -- with only a couple of minutes to go until her school board meeting for her daughter, Sawyer -- Brooke explained the reason for her call.
"I was just calling to make sure that my beautiful godchildren are registered to vote," Brooke, who's working hard on her fashion line, said.
"Brooke, how old do you think my kids are?" Haley questioned.
"Don't let her answer that," Peyton advised, before reading between the lines of Brooke's query.
"Brooke, are you using our children, who are clearly not 18 years old, to find out if we are registered to vote?" Peyton asked.
"Well, not no," Brooke admitted.
Peyton urged her "nutcase" pal not to change, before Brooke explained the importance of voting.
"It's register a friend day, I just had to check! I didn't want to shame anyone, but, you know, friends don't let friends not vote," Brooke said.
"That's good. You should put that on a campaign poster," Haley suggested.
"Do you think it would be better than my original slogan?" Brooke asked in response, as she held up a button for her high-school campaign with the slogan, "Brooke Davis: The Easy Choice."
"Stop it! You do not still have that," Peyton marveled. "She's a nostalgic little bunny. That's why."
After explaining the process of helping friends register to vote, Brooke told her pals, "Text me pictures of both of your faces and my godchildren because I miss you both very much."
All three women shared the video on Instagram, with Bush writing that they were "giving the internet what it deserves."
"P. Sawyer, Haley James, and B. Davis want you to text FRIENDS to 26797 to make sure you’re registered. It’s THE EASY CHOICE, after all ???♀️?♥️," she wrote.
"We’re baaaa-ack! Peyton, Brooke & Haley want you to VOTE! #RegisterAFriendDay Text FRIENDS to 26797 to register/check registration status," Lenz captioned the clip. "Friends don’t let friends not vote!"
Meanwhile, Burton said she was "so happy to reunite with my lifelong loves Haley James and Brooke Davis!!!"
While fans delighted in the mini-reunion, when ET spoke with Burton in May, the actress revealed what it would take to do a full OTH reboot.
"I’ve been working everyone behind the scenes. We all love each other. So, working out the business end of things would be the thing. I love those guys. I love 'em so much," she said. "We had trouble with our creator on that show. That is not a mystery, and so I think it’s all about ownership of the show and the politics behind that. Because there were a lot of abuses and so if we’re going to come back, we want it to be from a place of light and the good stuff."
"We have really hung on very tightly to the good stuff, which is why we do conventions, it’s why we support each other on social media. I think it’s probably the thing that forged all of our friendships," she continued. "You know, we went through something hard together. So yeah, if the politics get sorted out [I'd do it]. And by the way, they could go off and do any show on the planet and call me and be like, 'Will you show up?' And the answer would always be yes."