Blue tooth phone lock out

[ColinU]

When I start my 2005 S Type Sport 2.7 diesel the touch screen states Hand set in use. Mute and replace handset.

My iPhone 4S isn't even paired anymore.

I read somewhere that it is because the 4s isn't compatible and causes the lock out. It worked when I first had it then threw up this message which never goes away so I can't do anything.

Any ideas anyone.

Thanks

Colin