warwick, i see that you are easily confused but what appears to be employees of mera or nextone.
DO NOT MIX gatekeeper and billing servers with gateways.
As far as I know, Voicemaster does not have built-in gateway, while nextone, cisco, asterisk and mera are GATEWAYS or Softswitches with integrated gateways.
I was tricked by the MERA “softswitch”, and almost bought it. it is not, they claim they support 1500 calls, then they added protocol and codec conversion, IVR and othe gateway functionality, another words they add a module, but as they said it’s a hardware module, i.e. they add a gateway in the picture. With all the translatiuons and conversions, the cappacity went down to below 300 calls. Do your homework. make sure you know what you are looking for, gateway ot gatekeeper.