Asterisk MWI configuration for Voicemail

Hi all,

Can someone please help me in setting up a Message waiting indication service in Asterisk for H.323 adn SIP endoints .
1 What are the required configurations ?
2 What does the endpoints need to implement in order to recognize the MWI indications ?

Please provide your valuable feedbacks. Awaiting an earliest positive response.

Thanks in Advance,