txttools uses a web interface to allow users to send and receive text messages to multiple people, schedule a message to go later in the day, week, month or year, and track the delivery of the message to mobile devices. Their API allows programmatic access to txttools services using a SOAP and XML.
From their site: "Our clients are distributing information, scheduling meetings, sending appointment reminders and test results, changing arrangements, getting customer feedback and much more."
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