GSM-Shield does not show (pickup) a call ?

I can't get the genuine "Arduino GSM" Shield to work on a UNO R2.

Powerered by external 12 Volts 1000 mA and connected to my PC by USB.

I tried the Tools:

-"Test Modem" = Fine.

-"Band Management" = Yes.
4 : E-GSM(900)+DCS(1800) ex: Europe (Switzerland)
Configuring band EGSM_DCS_MODE

-"GSM Scan Networks" = Yes !
Scanning available networks. May take some seconds.
> Orange

  • sunrise*

    Current carrier: Orange
    Signal Strength: 19 [0-31]

So I tried: "Receive Voice Call",
but I commented out //vcs.answerCall();
because I just need the calling number. (If you're on the Guestlist, a Relais will powers the Dooropener)

But nothing happens, it just print out "IDLE", no Number.

What can I do to figure out what is gooing wrong ?

I power up, then after a while he sends "Waiting for a call" but does not show the Number.
If I press Reset on the Board, it's working ! Woo-hoo !

But not reliable... How can I make it rock-solid ? (What do you ?)