These notes are for the basics of setting up a few different ATA / IP Phone / Softphone VOIP devices and apps, SO THEY ARE SECURELY CONNECTED WITH TLS / SRTP ENCRYPTION TO THE SIP (VOIP) SERVER (so nobody can eavesdrop in on the audio data stream, as it travels across the internet), and a few other GENERIC security lockdowns / basic important setups.
The settings included here were all configured for https://voip.ms VOIP services (highly recommended!). Consult your VOIP service provider for additional settings to authenticate properly with their service. Some settings I explicitly mention here MAY need to be different, IF you are using a different VOIP provider.