Britney Spears broke down in tears during a Christmas Day phone chat with her estranged husband KEVIN FEDERLINE, according to US reports. Federline called to speak to wish the couple's sons, Sean Preston and JAYDEN JAMES, a Merry Christmas, but Spears couldn't resist the temptation to have a private conversation with her ex. And friends claim Spears became so emotional at one point, she burst into tears and told Federline how much she missed him. One pal tells American publication Life + Style, "She told Kevin the holidays were hard and talking to him made things harder because she missed him. "She was depressed over the holidays. At first, it was liberating for her to be free and single. But now she's in this big new house in Beverly Hills, and it's really lonely. "She invites girlfriends over, and her mom and sister spend a lot of time there, but, at the end of the day, it's just Britney and her babies. "When she first separated from Kev, she partied like crazy to numb the pain. Now the hurt is catching up with her."