[Freeswitch-users] Picking up voicemail

Hi, I have FreeSWITCH running over an internal IP network, connected to the PSTN line with an SPA-3102. When an outside (PSTN) call comes in, a Group of phones are rung until the first one picks up or until the caller falls over to voice mail and can leave a message in the Group Mailbox (100). I can retrieve the messages from any local phone - so far, so good. I'd like to be able to call in through the same PSTN line and interrogate the group mailbox, or any mailbox come to that. Can someone point me in the right direction for how to set this up please ? i.e., once FreeSwitch has answered the call and the voicemail prompts have stated, can they be interrupted so that I can get to the voice mail extension. regards Dave