I used the tubescreamer plugin (ts-9) and it worked a treat, also got that really gritty radio sound using the ts pluging along with heavy EQ filtering if that interests you
I've been using this for quite a while actually! It's great. And, I can definitely vouch for the fact that it is not PC only... I used the FXpansion VST to RTAS wrapper and it runs just fine with Pro Tools on my G4. Maybe there are different versions of rubytube floating around out there?
EDIT:
I didn't test the download button on this link, but it says there's a Mac version:
Thats from their page....If anyone knows where to find an AU version, Ill be a happy boy. I have been using VintageWarmer recently to satisfy my vocal distorting needs.
I just used the TSS plug on a blackened death band, gain pretty low, tone cranked. Really gave the high screams a brittle edge that sat nicely. I put it first in the chain, prior to comp, eq, verb etc
Speakerphone is a good one to try. I just copied the lead vocal track and used a heaviely distorted on speakerphone sound on the copied track and blended it in with the orginal clean one. Interested sound as when the vocal is more shrill the distortion interacts a bit more heavierly.