Have you tried Mo-call? Damn! Disappointed that they don't work yet. I was using Truphone previously, they do take long time to update their apps. I'm due to get my 9900 on 26th.
If Mo-call doesn't work, other option is vodafone UK do a intl calling add on, which is �5/month and you get discounted rates. Not very cheap comparing it to the apps, but loads better than �1/min. You could do an add-on for a month or so, until these apps start working. Find out if there's any minimum term for this add-on as I'm not sure.
Posted from my CrackBerry at wapforums.crackberry.com
belfastdispatcher - If you are still looking for an app for international calling, I've found voxofon which supports BB 7 OS. Just downloaded it and haven't used it yet.
Vopium for 9900 is in works, I think. May be this will tide you until they release update.