Thanks for your response.
Gateway in the sense, is their a need to configure it from our end
or
Can we get GW server from the ISP's end.
If GW server has to be configured from our end, hope we need to
install asterisk in a separate server and integrate asterisk
with opensips basing the link
http://www.opensips.org/Resources/DocsTutAsterisk.
right
Will this be enough for making outgoing calls.