Come Wednesday, Colbie Caillat will have a real reason to crack open the bubbly (every pun intended). On that day, Caillat will celebrate her second album debuting at the top of the Billboard 200.  "Breakthrough," Caillat's second album, shows impressive growth by the singer/songwriter, whose first album,  2007's "CoCo," sold more than 2 million copies in the U.S., largely on the strength of the evevescent  "Bubbly."

We caught up with Caillat a few weeks before "Breakthrough's" release for this interview for MSN Music. She's the first to admit that the last few years have been a total whirlwind with tremendous highs and a few lows as she went from unknown to everyone's favorite girl next door and Jason Mraz duet partner.

"Breakthrough" deals mainly with romantic entanglements, even though Caillat admits she's gone through having her heart stomped on by someone else:  "I've never had my heart broken. I don't take relationships too seriously, but everyone else seems to. And when you get your heart broken, it's like the end of the world. And I look at it as that was one moment in your life, one chapter. That person helped you grow and figure out what kind of person you want to be with in the future."

On the new album, she wrote with such top songwriters as Rick Nowels, John Shanks, and "American Idol" judge Kara Dioguardi, who taught her a little something about being fearless.  "The girl does not care, she will just sing any lick and she sings at the top of her lungs," says Caillat of Dioguardi. "I'm always shy and timid when I write in front of people. But, just observing her, I learned not to really care and just go full throttle when you're writing and when you're singing because people admire that."

Caillat draws inspiration from her life and from those of her friends for lyrics. For example, the title track is about a friend of hers who hasn't spoken with her father for five years. A song on "CoCo" dealt with another friend's unplanned pregnancy.

The  Malibu-based singer starts a new tour in mid-September. She previously dreaded playing live, but has grown to love it with a little help from her friend, Mraz-and 25,000 other folks. "I was just at Portugal at a festival and Jason Mraz was there. There were 25,000 people. We sang "Lucky" for all of them. We couldn't even hear ourselves sing because every one of them was singing so loud. I was like, "Oh my god, I don't even want to get off of the stage ..." I was giving [Jason] a hug to leave and he stopped me and he said, "Wait, just look out there and soak this up for a minute. We're going to be doing this for the rest of our lives." And I thought, "Oh my god, you're right. This is the start of something for a really long time."