NOTE: The SMSGTE server is gone but there's a new server: Server name is SMS and you must opt in your phone number first at www.theconnectdesk.com/SMS for it to work.
FTM-400 works the same way except easier to type in messages.
Today on HamRadioComms I show step by step how to send an APRS Message text on an FTM-300DR to a cell phone SMS message. The general format can be used to send using any APRS capable radio.