Now here's a turn up for the books...
"Although Apple blocks VoIP over the 3G network, Vopium has in fact got round this issue. When using the 3G network the call is signalled over a http ping via 3G or GPRS meaning the call is made as a normal local call to a local access exchange and not as an internet call. The call is then transferred to Vopium's servers where it is terminated in the required country at a local exchange. This enables Vopium to offer uninterrupted coverage and does not tie people to WiFi 'hotspots'. In this instance users may incur a local charge from their operators."
Now I'm tracking down what this 'local charge' may entail, but equally interesting would be whether Apple knows about this loophole and if so has it let through the Vopium app anyway? Should that be the case - expect fireworks. If not, will Vopium be pulled from the App Store in its current form?
We're chasing answers dear readers, but while it's out there go give it a try yourselves...
Update: Here comes some explanation (let me know if you'd like any more questions addressed)
With free calls from Vopium to Vopium and no way of checking who is online, how is this a better solution to Skype or Fring? Currently, Vopium iPhone users are able to see if the call has been free of charge or if they have incurred a local call charge.
Can you roam in and out of WiFi and 3G connections seamlessly? Apple doesn't allow VoIP and IP to be carried over data network, so users are therefore not able to flick between WiFi and 3G when using Vopium.
In related news Vopium has also become the first mobile VoIP application on BlackBerry App World. Off you go RIM fans.