Eventually got
Voip.ms going again after re-adding the device (after factory reset), re-adding
Voip.ms as a service provider (and having to go into expert mode to add the password), and re-doing the wifi.
IMO, Obitalk could do 2 things much better:
1) the setup to add
Voip.ms as a service provider could be much clearer. Having to remember to change the appropriate places in the Obi Expert mode (e.g. for the sub-account password), et al should not be needed; this should be done by the service provider setup wizard
2) ObiTalk should store configurations for you, and be able to re-install them to your device directly (without intervention) for cases like this when a software upgrade goes awry and a factory reset is needed.