There’s a donate button on the wiki. That goes to the project initiator who is not active anymore, and barely reachable. He does pay for some of our hosting services, but I have no idea how balance stands there. So I'm not sure if that's a good way to donate.
We've looked into joining organizations for funding, money and juridical/law support in the past, but never managed to decide and follow through [the application process].
We don't have members with Mumble as their job/main time spender, so even managing suggestions to changes can be difficult time-/resource-wise.
davide recently set up a bountysource salt account and wants to try establishing an income stream that would allow us to maybe spend some regular and paid time on the project, in his case establishing it as a career path, in my case potentially cutting down regular "job time" in favor of working on the Mumble project.
You can find that at https://salt.bountysource.com/teams/mumble-voip
Thank you for your interest.