Can't press number for menu selections during calls on snom d150

We resently got the SnomD150 to replace our old IP phones. The phones are conected to internet via Ethernet cable, but since out teleprovider  is a strictly mobileprovider, all phones have a mobile number (true number) and a landline number (number shown when dialing, same as old numbers). As I understand from them, the phones are not IP phones, but mobile phones disquised as IP phones (As a complete newbie I do not know what that means)
But we just cant figure out how to press Numbers for menu selections (Such as "press 1 for English") during calls.
Pressing the numbers doesen't work; pressing # first then a number doesn't work; Pressing * first then a number doesen't work; holding down either * or # and pressing a number doesen't work. All of the above does enter inn a * in the display as it should, but it does not register as pressing a number and chosing a menu selection during the call.
The manual for the phone is either of no use for this problem, or I cant find out where it says anything about it.

Theres probably some easy way to do this that I just dont understand. Can anybody help?