Cracking voice connection

i’m using a 3 com 24 port switch for my data and a 3 com hub for my voice solution. Both are connected into different nics on my server, the data cable from my radio goes into my hub as well…. the data is fine ‘cos am able to brows….the voice keeps cracking. By the way am using 2 different IPs, one for the voice and the other for data…(class A public..10.10.x.x and subnetmask 255.255.255.0),also a dns server is assigned and a default gateway. I’m using a net2phone IP phone. pls. i need help/solution on why there is no clarity on the voice….