I quote the information from Dr Wurzer:
Dear Community,
I would like to thank everyone who has ordered a Volla tablet. We are still in the process of delivering the pre-orders. Some of you have already received your tablet.
Unfortunately, we had to realize that the firmware of the first devices we shipped contained an error. The serial number and the IMEI numbers for the mobile connection (International Mobile Equipment Identity) are identical for each device instead of being unique.
This can mean that only one SIM card can be used at a time instead of up to two SIM cards, or that a mobile connection cannot be established. The Wi-Fi connection is not affected.
Our development team has already found a solution. With the next system update, the metadata of your Volla tablet will be automatically corrected. I apologize for the inconvenience.
I hope you enjoy your Volla tablet.
Marc Aurel