5200 security code

[Zarf]

do you have any idea how can i clear the security code for this phone?
How many incorrect retries can i do?

[Zarf]

http://www.newgeos.de/communicator/atari_9500/bilder/mtac3.JPG
no, i have THE VERY OLD Motorola 5200, which is shown on the picture.
I know that it's 100% working, I have a charger and the battery... but the last man who know the security code died some years ago. :) but i really want to make this phone working