Qtel never block any website/service dedicated for VOIP. It's became ilegal if someone selling vouchers or use Computer to sell the service to others peoples for phone.
If only for Personnal user, its fine as long as it use by them self not to re-sell.

Now the question, where its to buy the voucher, if ilegal to sell it? I believe the VOIP website offer the voucher through online, just buy from them.