There are issues with SIP and VOIP telephony currently affecting a number of SIP Trunk and VOIP Telephony providers across the UK.
Accordingly this will affect customers, suppliers, clients all over UK that use these services.
We suspect this is to do with the UK internet or telephony backbone in some way.
We will post again as the cause is determined and give an ETA for the fix.
**Edit 15:14PM GMT – Call connectivity is now restored** will post root cause if we find out