teltarif.de recently reported, that eplus (the network simyo & blau use) has recently started barring certain access numbers of call-through-services, after O2 did that before. I don't know if Betamax access numbers are affected yet on the eplus network, but O2 definitely blocks calls to most Betamax access numbers. So be prepared Betamax callthrough to become unavailable.

As far as i am informed they only barred dial in numbers for certain voice chat services but no access numbers for any calltrough providers.

Chris