Thanks for your report.

Recently we tested some SIM from AT&T and they are making it very difficult.

  • IoT SIM card can be used without any problem.
  • Voice & Data sim which is used in phone cannot be used.
  • Data only SIM need to lock IMEI. If you change the IMEI to the same that your registerred in AT&T it works.

Still trying to understand what is exactly happening.