Currently to view SMS requires to click in order to show the thread of a given number/contact. A "toggle" UI element (not an "accordion" one) would allow expanding one or more threads without leaving the reading list.
1) Implementing a toggle would allow users to display a given thread within the same index list instead of jumping back and forth with the added benefit of being able to work with messages of more than one contact.
2) Do not "crop" messages by default to show only an X number of characters from the last message in a thread. The reading list should let users with large monitors read 3~4 full last messages as there would be plenty of space on large screens to do so when Join has been "popped-out" into its own window. No need to click and go to a thread (or toggle to read if and when the reading UI will have implemented a toggle)