We're investigating reports of intermittent VoIP call and registration problems.
The cause of the problems was caused by the third party "Zoiper" service triggering 100s of new registrations against multiple phone numbers. This caused high CPU and delay in processing messages.
Zoiper is a softphone that many customers use - they have their own servers that act as proxy between the sopftphone on a customer's device and our VoIP servers. Something within the Zoiper system seems to have malfunctioned and caused all zoiper registrations to re-register many multiple times.
We're still investigating further.
The problem lasted a few minutes, we're making arrangements to increase the performance of our systems to help in future similar circumstances.