2120 means: "The originating subscriber is blocked from sending text messages." Log into My Sprint, go to My Preferences > Block texts to control those settings. Also, see http://community.sprint.com/baw/message/227240#227240 for how to block/unblock. If you do not have SMS blocked, please call Customer Care or send one of the Sprint techs posting in this forum a private message with your Sprint phone number. They have access to your account and can help.