Our community uses Ventrilo 2.3.0 as well as TeamSpeak2 server - all nevessary information about gameplay is here
DW.PL Faq
We use GameSpy, because it is a system which was natively intended to work with Dangerous Waters. It's not required however - players can join directly to host by IP, but it improves communication - its easier to organise the session when I have to explain some things once, not many times on different communicators.
Notice, that specyfing your preferred platform @ forum in thread related to date [like 4th, April, 2008] helps the host to prepare the scenario earlier. Unfortunately not all players specify it there.