Можно узнать IMEI и IMSI, правда на некоторых моделях с этим бывают баги.
Вот список основных флагов для GetProperty:
"microedition.configuration",
"microedition.platform",
"microedition.locale",
"microedition.encoding",
"microedition.profiles",
"microedition.hostname",
"microedition.jtwi.version",
"microedition.commports",
"commports.maxbaudrate",
"CellID",
"LocAreaCode",
"IMSI",
"IMEI",
"MSISDN",
"batterylevel",
"funlights.product",
"vscl.device.backlight",
"vscl.device.blink",
"supports.mixing",
"supports.audio.capture",
"supports.video.capture",
"supports.recording",
"microedition.media.version",
"audio.encodings",
"video.encodings",
"video.snapshot.encodings",
"wireless.messaging.sms.smsc",
"wireless.messaging.mms.mmsc",
"com.mot.carrier.URL",
"vscl.system.wakeupmode",
"vscl.system.silentmode",
"vscl.system.javasettingvolume",
"vscl.system.javasettingvibration",
"microedition.io.file.FileConnection.version",
"file.separator",
"microedition.m3g.version",
"device.software.version",
"device.model",
"microedition.pim.version",
"language.direction"