Check out the Camera MIDlet tutorial example at Forum Nokia
- it does just what you're asking. It's fairly straightforward to use.
The MMAPI has many optional parts, and one of those is the camera support. Don't assume that a phone that has a camera and implements the MMAPI will necessarily support the camera part of the MMAPI. In Nokia phones, the Series 40 phones do not support the camera part (if they support MMAPI, it is just for playing audio), but the Series 60 phones (except the original 7650) do support the camera part of the MMAPI. Even in Series 60, only the most recent phones support the camera's full resolution via the MMAPI (7610 onwards, I think, but I'm not sure).
I'm afraid I'm not familiar with the other manufacturers' phones