The problem is that Fring uses their server to achieve registrations much like VoXalot...
So your IPhone registers with Fring and Fring with BetaMax...as a result the Fring server IP is passed to BetaMax for a bunch of people...hence the FUP
If you've got jailbroken IPhones..take a look at
HowTo: Setup VoIP On Your iPhone - Voxalot FAQ