with my little knowledge about voip, as i posted in another thread
voxalot-support/4578-betamax-fup-again-2.html i have a spa3102 registered to voxalot, when i tried to make the call through voxalot with the betamax account added as a VSP in my voxalot account, they charged me for FUP
but when i make the call directly from the ATA using the gateways in spa3102 or by adding the betamax account directly in the dial plan, i had no FUP charges. so the conclusion for me is that voxalot was the problem.