You have to be in a fireteam for chat to work, at least for now. Bungie has stated they are working on more open chat. Likely they are concerned about people who are abusive in cha if it is full open world (rightfully so).
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Is there anything I have to do to enable this? Iv done lots of crucible and random strikes and have never heard anyone.
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You have to join peoples' team. Just being in a crucible team does not put you in a fireteam. Use the roster menu.