A landline call disconnects when the 60 free minutes with Office365 are used up. It should automatically switch to use paid credits.
When using the free minutes per month with Office365 a landline call disconnects when the 60 free minutes are used up and without warning. It would be much better to automatically switch to use paid credits if they are available.
Peter Lam commented
Experienced the same issue twice and contacted Skype support. However they claim that the ongoing call will continue and will be billed through credits.