i think its because of the BROKEN MESSAGES...... if you have accidentally deleted a broken message (during its completion). if you read it... it will still show a MESSAGE ICON on the home and when you unlock it...
A MORE SIMPLE SOLUTION:
(youre making simple things hard..
all you need is your cellphone..
do these simple steps...
1. if that happened.. just press DELETE button..
2. press SELECT ALL..
3. SELECT ONLY THE LESS VALUABLE MESSAGES or YOU CAN SELECT ALL IF YOU WANT.
4. then PRESS DELETE.
5. PRESS the HOLD BUTTON.. if it still shows '1 new message' last step is..
6. turn it off. or restart your phone.. (turn off then turn on).
as simple as that.. no need to use another cellphone...