I just picked up a West Marine VHF460 - and along with getting my MMSI number on BoatUS web site noticed that there is an approved TEST Coast Guard MMSI number that you apparently can use to test your radio... 

For more on MMSI numbers and DSC in general see http://www.boatus.com/mmsi/faq.asp

Here is more information on how to test http://www.boatus.com/mmsi/MM1.htm#q10

How can I test to make sure I have programmed the number correctly?

If you need to test to see if the DSC feature is working, do not test the red button as this will send out an illegal false alarm and cause an unnecessary rescue response!  Instead, you may run a test call to the nationwide Coast Guard MMSI number, 003669999.  Enter this number into your radio’s calling memory and select the “Test Call” option from the radio’s list of individual DSC calls, you can then press the “call” or “enter” key.  Your radio will silently hail the Coast Guard with a digital signal on channel 70.  If everything is working properly, your radio will almost immediately receive the Coast Guard’s acknowledgement of your call, providing assurance that both your radio and the Rescue21 system are operating properly. You must be boating in an area served by Rescue21 to use this test.  Alternatively you may also use the DSC function to privately hail another boater’s MMSI number so that they can verify what MMSI came up on their ID. The DSC functions do not work at all until an MMSI is programmed in. If connected to a GPS, the signal will also provide your exact coordinates. TowBoatUS Captains with DSC radios will do a radio check with you if requested.

PS While I haven't been able to test the radio -- being too far inland ... the radio is on sale for a few more days at WM... and includes a remote mic, charging station, spare battery pack, belt clip etc.  IMHO a nice package.   

Jay