If you need only to link a couple of places and you have fix,public I.P. addresses on both places (not trought NAT), there is a very cheap option that will give you four phone lines and do not need a gatekeeper.
There ia person on e-bay selling some Ericsson VOIP boxes. Very basic setup, but for a point to point with public I.P. addreeses it could not get cheaper or easier to setup.
I have a couple of them that i bought for testing and they do not work for me since I have dinamic I.P.addreeses.
If you are interested and already have ATA 186 ‘s we could work out a swap. Post your e-mail if interested and I will write or call you.