Ive decided to set myself a project of moving each of the 25 sites I develop/admin/support to VoIP for interbranch calls.

I am hoping to use to a centralised server to manage setting up the calls, with the actual voice data (RTP) going Point-to-Point. Any POTS calls should continue as they do now so that there is no need for me to use a SIP Provider. Is this possible with Asterisk?

A little more info:

Each site
* Is independant of the others.
* Has, at minimum, a 1mb ADSL connection.
* Has a DNS reversable address
* Has (at least for now) 1 POTS line that *needs* to be both VoIP and POTS.
* There is no VPN between sites.

My initial thought is to buy a SPA-3102 ATA for each site and configure said ATAs to use the same Asterisk server (internet facing) for call registration. I need to be sure though that the voice data will not end up being relayed via the server but will go PtP; none of the sites have the upload bandwidth to cope with the level of calls.

I have had a read through the Asterisk site but I cannot see anything about using Asterisk as a server for remote, non-VPNed, clients.

Any and all advice welcomed