Viber is no longer working on Alfa (Not sure about Touch) as the ministry has apparently stopped the service for all 3G subscribers. It is still working on Wireless connections though. Gino has some explanations as to why the service was stopped and how to bypass it. You can check them out [Here].
I think one of the reasons could be that Telecarte and Kalam cards will be back soon, if they are not back already.