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Pro It's secure
TeleMessage uses end-to-end encryption, with an additional encryption layer while data is in transit. It also offers a bunch of other security features such as PIN lock, time limited messaging and forward locking.
Pro Administrative access
An organization's mobile messaging can be managed by an administrator. That means admins can add, delete or suspend users and enforce messaging policies.
Pro Desktop and mobile software
While the solution includes an app, messages can also be sent from a computer or Outlook. It can send data messages, text messages, voice messages, etc (as long as there are enough message credits).
They've been in the messaging business for over 15 years. Not a start-up, and use carrier-grade infrastructure.
They offer a bunch of APIs that you can integrate with own apps to automate messaging.