I've been reading and using tweaks from XDA for a while now, and after tinkering with Windows Phone I think I've finally found something i can contribute.
I've managed to get my HTC HD7 to give a Flashing Green LED for a missed call using old Windows Mobile 5 tricks.
By navigating to:
Adding a string value called:
And giving it the values:
To break this down it does the following:
a = Activate Phone
v2 = Vibrate for 2 seconds
p = Play Ringtone
f300 = Flashing LED for missed call for 5 minutes
These are the values that i've chosen for myself. It makes the phone vibrate for 2 seconds before the ringtone kicks in.
I haven't found a way to keep the phone vibrating while it is also ringing, but I find having the flashing LED more of a benefit to me as I'm constantly in and out of my office.
The script value is fully customizable, and more values can be found here:
I hope other people find this as useful as I have.