I have seen this quite a bit. It always seems to be with sip session timers. Inbound calls have no issues, but outbound calls do have issues. It seems that certain downstream carriers are not getting all of the traffic needed from voipo's servers or the downstream carriers just have poor implementations.

I personally have switched all of my outbound calling to another provider due to the call issues with voipo outbound service. **Note I have seen this with other providers on and off, but voipo seems to have this issue more often than others**