One quick thing (I'm heading out)

Some phones with answering machine (Like Uniden) don't have the Visual Message Waiting Light feature. (It only works if a message is on the built-in answering machine) I know Uniden without answering machine work for Visual MWI. Both types will have a stutter tone when picked up and a message is waiting.

I will find a great link to the answer about Nid later, or someone will beat me to it!