As far as I know, the phone call is not confirmed, only rumor. Supposedly, there was a phone call made to the US around 3am the morning Natalee went missing. Rumor says it was from Natalee. Rumor says there might have been background noise (PVDS's neighbor's monkey howling) that Beth might have recognized when she visited the VDS home.
To my knowledge, all of this is unconfirmed.
Thanks. If true, I'm suprised Greta or Beth haven't mentioned it. Guess they have to be careful what they say and WHO they say it about :(