SIP Experts Here?

We (ThinkPenguin.com) are looking for someone with SIP expertise who could move us to a reliable VPS hosted solution with a reliable trunk. Preferably with good fax support (I know fax over SIP is generally not too reliable, again, any experts on the subject here?).

If there is anybody here with such experience / knowledge who thinks they are up to the task I'll post a detailed setup that we would like to have. It involves SIP to POTS with call forwarding to cell phone and SIP adapters and setting up voice mail boxes.

And we have a few things we want to accomplish in the process that may make this a more difficult project. We would prefer to stick to free software although it doesn't necessarily mean we have to use Trisquel. Trisquel may not be the ideal solution for the server. My main concern is we simply aren't dependant on any non-free software components and security and upgradability are taken into consideration.