I have this simple free service you can use. you can create you own keywords.
send [mogsm][yourkeyword] to 88147
subscribe your phone, text: [join][mogsm]
unsubscribe your phone, text: [stop][mogsm]
send text without the brackets [] of course.
http://mobiquio.com/playsms
user:demo pass:password
ICQ:268731675