This Caller ID issue reminds me of this thread:
http://forums.voipo.com/showthread.p...-being-blocked

They are spoofing the CID number field with text instead of numbers. I believe the "block all unknown calls" only looks at the CNAM field not the CID field. It's a good suggestion that Voipo look at updating their blocking feature to include this type of spoofing. In the meantime, adding an inbound call route as noted in the thread above seems to be the only way to block these types of calls.