Avril Lavigne's North American tour came to an end Thursday, leaving her with just a few more radio-sponsored shows to play before she can begin work on the follow-up to Under My Skin. But first, she needs to check her messages.

"I'm constantly thinking of stuff," Lavigne said. "In the bus, my hotel room ... Sometimes I'll just come up with a guitar part. Every once in a while, I'll come up with a melody, and I'll throw it down on my cell phone. If I'm out and don't have a tape recorder, and I have a song in my head, I just call my cell phone and record it."

She's been on the road almost continuously since Under My Skin dropped in May, so there surely must be at least one future hit on Lavigne's voice mail. In February, she'll look for another when she gets back together with Butch Walker, the singer-producer who's been serving as her opening act, in an attempt to rekindle the successful songwriting collaboration that yielded her last single, "My Happy Ending."

"Butch is really awesome, like a really good guy, so I thought it would be cool to bring him out," Lavigne said. "During the day, when I get up to do radio-station interviews and acoustic performances, he's been coming with me -- and he doesn't even have to. He just comes and plays guitar with me, does background vocals and harmonies. It's been really cool."

In the new year, Lavigne will have just a few weeks to work on the album before launching a Japanese tour in March, but she's in no rush to finish it. After all, Under My Skin is barely six months old, and in that time, it's spawned three singles with a fourth on deck.

"There will be another video," Lavigne said. "I think I'm going to come out with 'He Wasn't.' All the singles have been kind of serious, and I feel like I want to come back out with a faster, edgier, more fun, upbeat song -- something to rock out to."

That high-octane description suits the singer, as well -- she's spanned the globe in the past year, with concerts, videos and awards shows along the way. One might assume that some rest is in order sometime soon.

"Probably not," she replied. "I'm the type of person who likes to go-go-go. I can't stand sitting at home."