The download from 3CX does not include a ROM file for T58A phones, yet they are marked as supported. Phone is provisioned but shows firmware not supported. Currently running latest from Yeahlink (58.83.0.5).
That worked. Issue resolved. The download previously used was from the "here" link within the supported phones document. I am a new user and was not aware of the location you provided. Thank you for your help! Much appreciated!!