Dear Ancient Yardgnome,

You can do either.  That is, you can send a message to another 10
digit mobile number (text messaging) or you can send to an email
address.  The email address can be anyone's email address in the world
including another mobile phone.  But for short messages, "text"
messaging has less overhead (no "from", "to", "subject" lines, etc)
and is faster and easier to send.  Depending upon your particular
Cingular plan, text messages may be free or it may cost 10 cents or
more per message.  You may or may not be able to send a text message
to mobile number outside the North America.

And then there's IMing and MMS messaging, but that's another chapter.

Try looking at the online manual or, even better, your good old
fashion hardcopy manual that came with your phone.

http://www.motorola.com/mdirect/demos/v60i/v60ig_mim/userguide.swf

P.S. Questions like this are often answered in a somewhat terse
manner. You may receive responses such as "RTFM" and/or "Google is
your friend".    Now don't ask what "RTFM" mean without first going to
Google doing a little homework.

Good luck, in no time you'll be texting your grandkids.

SM

Here's a link to the PDF version of the manual.

http://www.motorola.com/mdirect/manuals/V60i_GSM_Manual.pdf