I have 2008 Altima – The cell phone does not stay paired with the car sometimes but becomes disengaged for no apparent reason.I have to pair the phone all over again. Can any one tell me why it does this or how to prevent it?

What kind of phone do you have? It makes a big impact...

I have a "LG VX8100" any help would be appreciated

The problem might be that your phone only has bluetooth 1.1, and its technically not compatible with the altima bluetooth system.

http://www.nissanusa.com/bluetooth/find.html

That gives you the rundown of all the phones that you can pair with the car bluetooth systems - unfortunatly, yours does not match.

The only solution right now is to use a different phone, as there is no hardware update for the car system to recognize older bluetooth versions on phones.

So why does it work(stay paired) with the car bluetooth system 80% of the time.

Because in the end it's still bluetooth - the connection "idea" is the same, there are just little odds and ends that have changed when the versions have changed over.