Turned out to be a STUN configuration issue, thanks for the help.
They don't mention the need for port forwarding in the Configuration Guide, but that's what did it. Strange that one phone worked fine and the other did not.
I am running
Standard Annual 18.0 Update 2 (Build 314) hosted by 3cx
Callcentric SIP Trunk
FW 150.86.0.5 on the T58W Provisioned using STUN
Both phones show up under the "Phones" section of 3cx with their respective extensions.
Activity log when attempting to call EXT 0100 from ext 1001...
I am testing 3cx for our office using a T58W (EXT 0100) and a T46U (ext 1001)
The T46U works great, but the T58W will not accept calls. The extension will ring on my softphone, but not on the T58W. I can call other numbers from the phone, both internal and external, but the phone will not...