I used a long time the Smartglass app on computer because you can copy/paste from a textfile but my problem with that was that the smartglass app needs a reconnect or restart sometimes and its not very responsive so its not perfect.
A cmdr explained to me that a USB keyboard works too and its so much better because you can write messages without to open the textwindow from xbox and still have control over your ship and its still very fast to write. Another good thing is you can switch your chatpartner with TAB, the same if you are in a wing, you can easy switch to local chat.
You can do that with switches
/l <message> sends to local chat
/w <message> sends to wing
/r <message> replies to the last person to contact you
(thanks Error)