[M_Grey]

To be fair, I'm not sure that Islam is too enthusiastic about atheists proclaiming for it either... to put it mildly.

[mturmon]

"There is no god but God" does seem to offer some wiggle room for atheists, but maybe that's an inadvertent loophole.

[M_Grey]

It might, but I think the current climate in much of the Islamic world, while not the crazed image many have, is actually pretty brutal to people within the religion who are seen as blasphemous. From what I know, and I have to admit that this isn't as much as I'd like, the process of proclaiming your faith pretty much involves accepting the existence of god, prophets, the "punishment of the grave," that kind of thing. My impression is that if you're seen to have lied about that, you're lucky just to be outcast.

tl;dr It really doesn't pay to be seen as an "apostate" in Islam, at least in most places at this time.