Richie and Hilton
08/09/2007 AT 10:00 AM EDT
They've been friends for most of their lives – despite a two-year period when they didn't speak to each other – and now Paris Hilton
is sharing in Nicole Richie
's baby excitement.
"She's really happy," Hilton, 26, told PEOPLE about her Simple Life
costar at Wednesday's Helio Ocean launch party in West Hollywood, to benefit Heal the Bay. "I just got off the phone with her. She's so excited."
Adds the hotel heiress, "I know she's going to be the best mom ever."
In a series of ABC interviews last week, Richie, 25, told Diane Sawyer that she is four months pregnant
with musician boyfriend Joel Madden, 28.
"They're really in love," Hilton says of the expectant parents.
Not that all is hearts and flowers for the mom-to-be.
Due to serve four days
in a L.A. County jail, for a second DUI conviction (she must put in her time before Sept. 28), Richie will likely be kept at Lynwood, Calif.'s Century Regional Detention Center – the same lockup
where Hilton spent 23 days earlier this summer.