Dezmaas,
Internetcalls.com are run by a Germany or Swedish company called
betamax. They run 15 clones of voipcheap, internet calls being one of them.
http://www.sipdiscount.com
http://www.internetcalls.com
http://www.voipstunt.com
http://www.voipdiscount.com
http://www.voipbuster.com
The issue your describing is a common one with people using VoIP and isn't provider specific. Im not 100% sure, but i think it's due to the fact the most old answermachine are touch tone, and when calls are routed via VoIP the answer machines can't understand. Perhaps someone will elaborate more or correct me...
Matt