Does Comcast offer a Better Gateway router than the SMC SMCD3G for those that have Static IPs?

 We have locations at 3 sites. 2 are  Comcast Business Internet.

Both sites have the SMCD3G. I am having trouble with VOIP services.

At one site the VOIP phones are using our router the SMCD3G is of course passthrough on the IP.

The other site is split out. The network that is used by the office for internet is same situation our router and the SMCD3G is passthrough on the Static. But the phones are connected to the SMCD3G through a switch and are using the dynamic IP and getting their settings from DHCP on the SMCD3G.

So the common denominator is the Comcast service and the SMCD3G.

VOIP provider  is pointing to Network being the cause of incoming Calls will ring and phone will not anser when picked up it takes picking up the phone 2 or 3 times for the phone to connect the call.

I am curious if I have the best equipment offered by Comcast when it comes to having Static IPs and having to get our Gateway Router through Comcast.

Any thoughts?