Here is a quick bit of documentation for special dial prefixes available to you.

Dynamic Groups
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Dynamic group extension where members can join the group and leave the group by dialing pre-defined access codes.
i.e. *JOIN2000 *5646 2000
i.e. *EXIT2000 *3948 2000

Voicemail
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Check voicemail
i.e. *MAIL2000 *6245 2000

Alternatively you can check voicemail by dialing the voicemail extension directly, i.e. 2000 from your SIP phone connected to your PBX and immediately hitting zero.

Audio
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Playback and Record audio special extensions
i.e. *PLAY2000 *7529 2000
i.e. *RECO2000 *7326 2000