If you have a static,public I.P. address on the gateway, does it not take too long to make it call out.
That is from the gateway to the VOIP provider.
If you are behing a firewall or a NAT router, it will a lot more dificult, and may not work at all.
If you have the above, public and static I.P. address, i could set your gateway for outgoing calls for free.
Contact me at email@example.com