Mitel 3300icp and standalone Asterisk Voicemail

We currently are using a Nupoint Messenger voicemail server that is literally on its last leg. My 3300icp is at software version 7.1. I am looking into the possibility of replacing it with an Asterisk box and use it only for voicemail. My question is what would be the best way to connect the systems (SIP,T1/E1, etc) and will MWI work over each connection. If anyone has already done this, a config example would be great. Thanks in advance!