So, the answering machine is poor man's voicemail for Ext. 10? You could try the answering machine in its own extension port, not twinned with a Partner phone. See if it will answer when you call it, and see if Distinctive Ring makes any difference. If you get it answering when Intercommed, you could use Call Cover from 10 to the Answering Machine's extension number to still provide coverage for 10, and you could put line appearances on the answering machine's extension port to answer incoming calls on a delayed basis as well.