So it seems i am finding alot of things that you just can't do which I thought was basic things that went into a mmo :(
Kinda discouraging
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You can send tells in this mmo, as well as trade, just not in a duty.
People have gone over SE's reasoning for tells
The trades I can see as well, let's say you are a healer on a non legacy server, and you queue up for a dungeon that not a ton of people do. At the same time a friend of yours from a legacy server queues up for that same dungeon as a tank (dps would be more difficult to get this done with) at like 1-2am PST. You could do this until you get into the same dungeon and your friend off of the legacy server with the legacy account could just hand you a ton of stuff you couldn't possibly have yet (which is why legacy servers are separate and probably won't be able to xfer from for a very long time).
Just an idea, might not be right...
Tells don't work simply because when you're in Duty Finder, you're literally not on the server any more. The instance servers are separate (they're the things that initially overloaded) and when you're in a dungeon or wherever, you're playing with people from different servers. Your friends will also see a "Not in this world" icon next to your name on their friends list as well.
The trade is disabled for just that reason too, it could destabilise the economy of the worlds if it allowed transferring of items between worlds.
Hope that helps to explain!