Android 2.2 (Froyo) and above
http://blog.naver.com/schweine7?Redirect=Log&logNo=40119300243
http://www.cyworld.com/gurispace/3211763
http://blog.muik.net/archives/539
http://code.google.com/intl/ko/android/c2dm/index.html
http://jnylove.tistory.com/368
http://joejeon.tistory.com/310
http://okgosu.net/zbxe/tip_android/24530
http://blog.digitalstruct.com/2010/11/21/android-c2dm-with-php-and-zend-framework/
http://www.androidside.com/bbs/board.php?bo_table=B46&wr_id=14705