Technical display shows "10000000" while using the mobile handsfree

[Boekie1973]

in my Fiat Tipo on the radiodisplay and the cardisplay appears the number "10000000" while I'm calling handsfree.
I can not see other information but only the "10000000"
can somebody explain me what this is and how I can solve this problem ?
it's only while calling handsfree incoming and outgoing. 100% repeatable.

thanks

Pascal from Belgium