Hi!
Yes, there is such functionality to reject incoming calls.
First, you will need to navigate to Service > SMS Utilities:
Select Call Utilities tab:
And then select your action - what do you want to do with an incoming call:
NOTE: that this kind of configuration example is taken with changes that will come with 6.7 firmware (the next one, that should come out in a few weeks). 06.06.1 (current FW) is also capable of this feature, but the last page configuration looks a little different but should do the same trick.
EB.