What's the adapter at the side of the sim slot?

hello,
just opened the sim compartment and noted another slot, but its not sd, what is it?

There are two slots on the tray:
one for the MicroSD card, the other for a SIM card.
The SIM card works with respect that it recognises and shows a mobile network on your desktop, but it has currently no use, ad far as I know you cannot use a data connection yet.

Ehm did you try to put an sd card inside? i was unable to…

Yes. Works fine. Reiterating its a MicroSD card slot.

@bboett see spec, is a SIM + MIcroSD Slot:

I have been able to get this working on my device though it goes in and out sometimes.