That utility app is an unofficial public app from RingCentral Lab. One can use it occasionally with their own production account credentials provided that the account has a TF SMS number (otherwise, the "from" number list will be empty). Since it is your account TF SMS number, you will bear the cost of sending SMS from the app. The app is still using the normal /sms API which has the API rate limit at 40 messages/ minute. But the app will handle the rate limit itself so you don't have to worry about it. Thus, sending 1000 messages would take about 25 minutes to complete, and it will cost you $7.
Soon we will release a new app using the High Volume SMS API which is capable of sending up to 3 messages per second. The new app can be use with the same TF SMS number.
