We've had reports that calls from Vodaphone to some of VoIP numbers failing. We are contacting the carrier involved to investigate this issue with Vodafone.
This does seem to be affecting just one of our upstream phone number carriers and from Vodafone. Investigations are taking place.
Update from carrier; We continue to search for a pattern here but so far we have 'good' and 'bad' calls through various routes and paths into and through our network - we are just trying to narrow down what the common factor may be.
Our upstream carrier are still investigating. However, they have many examples if working calls and not so many of failing so this seems either intermittent or affecting a small set of numbers for some (as yet) unknown reason. If our customers have examples of failed calls, then please email support. We'll need time, the caller's (Vodafone) number and the called number that's failing.
This problem seems to have gone away, but with no actual cause of the problem being identified.