After firmware update (T46G), No Service, can't login

[Cory]

Thank you for the information.
What finally worked was to do a forced reset by holding the speakerphone button while powering on... then power cycle without the network connected.
After that, we could login with default credentials... sounds similar to what you suggested.

Once they reset to factory, we could do a little with them (login), but they both still had some weird traits... so we installed the Yealink 28.81.0.25 firmware again to make them fresh.
That seems to have worked, so far.