I can confirm that certification is NOT required for connection to the network. I have tested various uncertified modules to connect to Telstra's network.
I spoke with an IoT engineer at Telstra today and you are correct @Sat , Telstra do not block devices. However, the engineer was aware of the Pycom devices and stated without prompting that they have a "firmware" issue and that's why they won't connect, it is nothing Telstra side. I tried to dig deeper but he could not give any specific details other than a firmware issue with the current Pycom LTE devices.
**EDIT**: I spoke again with Telstra and they believe the issue is with the firmware on the Sequans modem.
Looking through the forums here I saw that the APN name "internet" is hardcoded in? According to my sim supplier the APN for Telstra's IoT network should be telstra.m2m (or alternatively telstra.internet). The Telstra engineer confirm this needs to be set correctly and could be causing issues.
I am good working with python but my ability to easily update and recompile the firmware for a FiPy is lacking... Is there someone out there that could do a quick check to see if this fixes the issue? Or at least give the option to specify the APN on the LTE.init() function?