Kevin Mukbel sent this tip: "Did you know that you can convert single-line text or more to multiline Mtext? Here is how you do it: On the AutoCAD command line type txt2mtxt, select your single line(s) text and you are done. TXT2MTXT will work on any text objects created with the TEXT or DTEXT commands.
This is an Express Tool. You don’t have to remember this txt2mtxt command. You can go to the Express Pulldown Menu | Text | and choose “Convert Text to Mtext”.
Notes from Cadalyst Tip Patrol: Text to Mtext is my favorite command from Express Tools. It will convert single line text objects (not Mtext that is all on one line but dtext only) into mtext and combine them if more than one is selected. If you are running AutoCAD 2009, the Express Tools are not in the ribbon. You can get to them by turning the menu bar on (the setting is menubar) or just type the command as stated above on the command line. Tested in AutoCAD 2009