[mvoigt],
It depends on the CLDC/MIDP runtime environment implementation of the MID device. Some manufacturers' might include additional APIs to allow such functions e.g. retrieving device specific information such as phone numbers or device numbers, however addition of such APIs will mean that the MIDP implementation for these devices is not 100% compliant to the standards.
It is best that you check with the device manufacturer and enquire about such additional non-MIDP compliant APIs.
HTH.
Allen Lai
Developer Technical Support
SUN Microsystems
http://www.sun.com/developers/support/