There is a PMS tester utility that can be found on Mitel online that I am told works with Win7 but I have not been successful in getting to work since XP. If you can get a copy and get it to work this is by far your best bet.
Otherwise, the manual process is very cumbersome.
Here is a string that would check in room 101 for example (just the first line, the other is to show the spaces and character count)
[PRE]
^BCHK1 101^C
^^^^^^^^^^^^^^
12345678901234
[/pre]
Checkout would be
[pre]
^BCHK0 101^C
^^^^^^^^^^^^^^
12345678901234
[/pre]
With voicemail there is a required checksum after the ^C. Believe me when I say, you don't want to go there
Get a copy of the program, it is priceless.
**********************************************
What's most important is that you realise ... There is no spoon.