Its an issue with the phone software...I've got the same issue with my Treo.
What I've discovered is that sometimes the phone will turn off the bluetooth function after I turn the car off. If I can't pair - or if I lose connection - I go into my phone and sure enough the "bluetooth" function is unselected. I just reselect it and refresh. Then I pair up again no problem.
I talke with BMW service this Monday and they said that future updates will resolve the pairing issue. But it may be a while...
Hope this helps.
[His] 2006 750i Sport - Jet Black, 21" wheels, premium sound, luxury seating, convenience, comfort access, Sirius (Jet)
[Hers] 2008 650i - Metallic Black, Sports, Prem Sound, HUD, HD Radio, Cold Weather, Sirius (Shiloh)
Moved on from:
2005 645Ci (Ava)
2004 545i (Chief)
2002 330i (Kira)
1998 528i (Slick)
1999 540i (Sly)